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Introduction
This article contains everything you need to know about aluminum forgings, including how they are made, how they are used, and the types of aluminum alloys.
You will learn:
What is an Aluminum Forging?
Types of Aluminum Forging
Uses for Aluminum Forgings
Types of Aluminum Used for Aluminum Forging
And much more…
Chapter 1: What is Aluminum Forging?
Aluminum forging is a method for processing aluminum alloys using pressure and heat to form high strength, durable products. The process of aluminum forging involves pressing, pounding, and squeezing an aluminum billet, workpiece, or cylinder under great pressure to create parts that have high strength. The temperatures for aluminum forging vary between temperatures that are below the recrystallization level to ones that are slightly above the recrystallization level or are ambient room temperatures.
The forging of aluminum includes all of the different forging processes, such as open and closed die forging and rolled ring forging. The choice of which forging method to use depends on the type of product to be created and how it will be used. In all instances, aluminum is ideal for a wide variety of applications due to its lightweight, strength, toughness, resistance to corrosion, and ability to be forged.
The forgeability of aluminum alloys is compared to that of carbon steel and low alloy structural steel. At room temperature, aluminum alloys have low deformation resistance compared to carbon steel, which has three deformation temperatures. A common characteristic of aluminum alloys in regard to deformation resistance is their sensitivity to temperature, which changes with increasing and decreasing temperatures.
Although casting of aluminum is a popular shaping process, forging of aluminum adds deformation energy that refines and improves the metallurgy of the finished part. Forging shapes and reshapes the internal microstructure of aluminum ingots crushing and eliminating voids and porosity. The energy of the process drives recrystallization of the microstructure to enhance the durability and toughness of the final product.
Chapter 2: Types of Aluminum Forging
The choice of the forging process for aluminum is to ensure that components have all of the positive properties of aluminum where weight and mass must be minimized and reliability is a necessity. The manufacturing definition of forging is a process that involves shaping and forming of a metal using compressive forces. The concept that is at the center of forging is the use of pressure to force a metal into a specific shape to match the dimensions of a component or part.
In general, forging is used to deform metals that have been heated to just above or below their recrystallization temperature or ones that are shaped at room temperature, which are the distinctions between hot and cold forging. From these two general categories, forging breaks into several different methods including drop forging, press forging, upset forging, roll forging, rolled ring forging, and isothermal forging. The choice of method for the forging of aluminum is carefully selected to meet the requirements of the final application and the type of aluminum.
Cold Forging
The various aluminum alloys are easily forged into complex and intricate shapes. Aluminum can be forged without scaling, using lower pressure, and dies at the same temperature as the workpiece. The cold forging process takes advantage of aluminums plasticity, which is the ability of a metal to undergo permanent transformation at room temperature.
Although aluminum can be shaped by cutting, the cutting process is time consuming and leaves wasteful shavings. Cold forging takes less time and does not produce shavings. The process can produce complex designs, intricate shapes, and parts in two dimensions without the need for secondary processing. Holes, chamfers, pins, fins, and steps are created by the cold forging process in one operation.
The basic principle of cold forging is to deform an aluminum billet, bar, or workpiece at a temperature that is below its recrystallization temperature, which is near or at room temperature. It is a cost-effective manufacturing method designed to produce complete aluminum parts that necessitate little or no finishing. Vertical presses that operate manually or automatically are used to apply a significant amount of pressure on a workpiece that is placed between an upper and lower die until the workpiece takes the shape of the die.
The deformation process changes the size and shape of the workpiece. A wide assortment of parts are made of aluminum using cold forging including alternators, gears, starter motors, motorcycle parts, hollow shafts, valves, switches, and anti-vibration parts.
The Benefits of Cold Forging Aluminum:
Interchangeability and reproducibility
Smooth even surface finish
Precision dimensional control
Assignment of targeted properties
Heating is not required.
Hot Forging
When aluminum is hot forged, the process enhances the properties of aluminum to a strength to weight ratio that is greater than steel. One of the reasons that manufacturers choose hot forging is the different selections of surface finishes the process produces, which range from very smooth and even to sharp and uneven, a selection that is quite different from that produced by cold forging. Several industries choose hot forged aluminum components due to their cost effectiveness, appealing appearance, and design flexibility.
In the hot forging process, aluminum is heated to its recrystallization temperature, 350°C up to 500°C (662°F up to 932°F) and pressured by forging equipment that pound and hammer an aluminum workpiece into a die. The final product from the process has enhanced strength and durability with a reduced grain size. The lightweight, high strength to weight ratio, and thermal and electrical conductivity are properties produced by hot forging that make the process so popular.
The keys to hot forging are heat and pressure. The high temperatures of hot forging are maintained throughout the process to avoid strain hardening during deformation. Additionally, in order to maintain the high temperatures, forging dies are heated to the temperature of the workpiece or slightly below the elevated temperature. During the forging process, the aluminum workpiece is altered as it is hammered or stamped multiple times until it achieves the desired shape. The heating of the dies assists in the flow of the aluminum.
Drop Forging
Drop forging hammers an aluminum workpiece between the halves of a die and is used for mass production of aluminum components. The upper half of the die is attached to the hammer while the lower half of the die sits on the anvil. The heated aluminum workpiece is placed in the lower half of the die on the anvil. Using continuous pressure, the workpiece is placed under compressive force until it fills both halves of the die cavity. During the squeezing of the workpiece, excess aluminum exits by being squeezed through the meeting points of the die halves. This unprocessed aluminum excess is referred to as flash and is collected to be reused.
The lightweight of aluminum alloys makes it an ideal metal for the drop forging process. Only certain types of aluminum can be shaped using drop forging and are mainly from the 6000 series of aluminum and the 7000 series of aluminum. At the end of the drop forging process, flash is removed from the workpiece, and it is subjected to secondary treatments.
Drop forging enhances the strength, toughness, and fatigue resistance of aluminum. Since it is a highly controlled process, deformation ensures dimensional accuracy and uniformity. Drop forging is a cost-effective process that has limited waste and capable of producing intricate and complex shapes.
Rolled Ring Forging
The process of rolled ring forging is designed to produce seamless rings from billets or cylinders. Rolled ring forging begins with upsetting a billet, a process that reduces the height of the billet while it increases its diameter to the point that it reaches the dimensions for the final ring. Rolled ring forging is an open die method of forging where the billet is heated to a temperature above the recrystallization point.
Upsetting prepares the cylinder or billet by deforming using horizontally applied pressure along the aluminum workpieces length axis. The force of the pressure allows the cylinder to spread beyond the area of the press. In preparation for upsetting, the workpiece is heated, which causes changes in the metal's grain structure and makes it softer and ductile.
In order to roll forge the workpiece, it has to be pierced to place a hole in its center, a process that is completed by punching or shearing. The end result of the process is a large donut shape that will accommodate the mandrel and rollers that will squeeze and shape the workpiece into a large ring. Rolled ring forging is referred to as forging due to the fact that the workpiece is not drilled, ground, or bored but is reshaped by force.
The piercing process creates a hole in the workpiece such that it can fit over the mandrel of the roll forging mechanism. The mandrel, also known as the saddle or idler, is made of steel and has the strength, durability, and resilience that is sufficient to withstand the pressure and stress created by rolled ring forging.
For the workpiece to be deformed using rolled ring forging, it has to be heated to a point below its recrystallization point to make it pliable enough. In very slow steps, the work piece is rotated and forced against the drive roller to change the workpiece’s inner and outer diameter (ID and OD) to match the dimensions of the final part. As the workpiece turns, the mandrel applies pressure to the interior of the donut against the main roller to make the walls of the ring smaller.
The toughness, tensile strength, and fatigue resistance of aluminum makes an ideal metal for rolled ring forging. In addition, unlike most other metals, forged aluminum has an excellent surface finish that is visually appealing and exceptionally smooth. Aluminum rolled ring forgings are used as parts of jet engines, jet turbines, windmills, paper mills, helicopter gearboxes, and tools for hazardous conditions.
Open Die Forging
Open die forging shapes aluminum using dies that do not completely enclose the aluminum material. In the open die forging process, an aluminum billet is stamped, hammered, and pummeled until it takes the shape of the die. Since the material is not completely enclosed in the die, completed components receive secondary processing to achieve the desired shape. The process of open die forging is used for the production of discs, sleeves, cylinders, and shafts that are simple and uncomplicated.
The purpose of open die forging is to enhance the grain structure of aluminum components because of the repeated blows to the aluminum billet. An additional benefit of open die forging is improved fatigue resistance and strength that is added to aluminum products. As with many forms of aluminum forging, open die forging eliminates voids that can limit the effectiveness of a part.
The workpiece in open die forging is allowed to move freely, laterally, which makes it possible to forge very large parts weighing several tons. It is ideal for short runs and custom products and is used for rough shaping ingots for further processing. Additionally, open die forging improves aluminum’s ability to be machined. Aside from components having improved resistance to wear, open forged aluminum has improved mechanical properties that are similar to those of machined and cast products.
Closed Die Forging
The process for closed die forging is very similar to that of open die forging with its variation being the function of the die. While the die in open die forging does not completely close the workpiece, in closed die forging, the die halves completely close and encompass the blank or billet in order to produce the final product. Closed die forging can be completed in a single stage or multiple stages depending on the type of product and its complexity. The types of alloys for aluminum closed die forging are heat treated to different temperatures depending on the type of alloy and its composition.
The process of closed die forging involves working the blank or billet between the upper and lower halves of the die with the lower half resting on the anvil while the upper half is attached to the hammer. The degree of deformation is controlled in order to break down the microstructure of the billet or blank with the grain flow in the direction of the stressing.
Due to the cost of closed die forging dies, the process is used for high volume production runs and has exceptional dimensional accuracy. Control of the grain flow makes it possible to use secondary machining to reach closer tolerances. Every product produced by closed die forging has consistent dimensional accuracy, which drastically reduces the amount of secondary finishing. Closed die aluminum forging produces forgings with good mechanical properties and structural integrity.
Closed die forging is an economical method for producing large production runs. Its cost efficiency is further increased with the elimination of machining and an increase in the rate of production. As with many aluminum products, closed die forging produces products with a high strength to weight ratio with a wrought structure that is shock and fatigue resistant. Voids and porosity are eliminated such that products have a smooth even surface.
Leading Manufacturers and Suppliers
Chapter 3: Types of Aluminum Used for Aluminum Forging
The choices of aluminum for forging are ever growing due to aluminums lightweight, resistance to corrosion, and exceptional strength to weight ratio. It must be understood that not all aluminums can be used for forging, which necessitates careful selection of the type of aluminum to be used for a project. There is a long list of aluminum alloys that can be used for forging with the 6000 series and 7000 series being the most common ones.
An aluminum alloy chosen for a project depends on a select group of factors, which include the application for which a product was designed and the properties the product must have. There are six specific factors that need to be considered when choosing an aluminum alloy.
Cost – Although cost is an obvious consideration, it may not be the most important part of the selection process since the design and nature of a product may require a higher quality of aluminum alloy. Manufacturers work with their clients to assist the clients in selecting an aluminum alloy for forging that is economical and is the best fit for a client’s needs.
Strength – Forged aluminum parts that will be subjected to stress, heavy loads, and harsh conditions require high strength alloys that are capable of withstanding the load requirements and conditions.
Corrosion Resistance – All aluminum alloys have corrosion resistance to a certain degree. Although this is true, certain alloys have lower resistance due to the compounds used to produce them. An evaluation of the environment where a product will be used can be a major determining factor when choosing an alloy.
Weldability – The weldability of aluminum alloys varies from very weldable to unweldable in certain conditions. The factors that make welding aluminum difficult are its oxide layer and thermal conductivity, which influence the level of heat energy necessary to weld aluminum. During the initial selection process, manufacturers learn whether welding will be involved in a project and assist clients in selecting a weldable alloy.
Machinability – Depending on the forging process and the design of a product, some aluminum alloys may necessitate machining to achieve the required tolerance. There is a wide selection of aluminum alloys that can be machined, to a certain extent. The amount of machining plays an important part in which alloy to choose.
Thermal Properties – Most aluminum alloys have good thermal conductivity, which is three times greater than that of steel, a factor that makes it an excellent material for cooling and heating applications. Various grades of aluminum alloys are excellent at dissipating heat, making them ideal choices for applications that require the removal of heat.
Aluminum Alloys Used for Forging
As with other metal forgings, there are several aluminum alloys that can be chosen for the manufacture of forged products. In the 170 years since its introduction, aluminum alloys have become the most widely used industrial metal with several million tons of it being used every year including new and recycled aluminum. A careful study of the various aluminum alloys and their properties can be helpful in selecting the right aluminum alloy for a project.
Aluminum Alloy 6061
Aluminum alloy 6061 is part of the 6000 series of aluminum alloys that have the number 6 indicating that the primary alloys in the series are magnesium and silicon, which are present in greater quantities than the other alloying elements. The composition of 6061 is 98% aluminum, 1% magnesium, 0.6% silicon, 0.28% copper, and 0.2% chromium with an assortment of small quantities of other elements.
The characteristics of aluminum 6061 include weldability, machinability, corrosion resistance, and workability. The different tempered grades of aluminum 6061 are 6061-O, 6061-T4, and 6061-T6. The letters and numbers after 6061 indicate the level of tempering the alloy has received, which is how it was heat treated, cold worked, and aged with O indicating that the aluminum has been annealed. The T4 and T6 grades have increased yield strength due to their tempering.
Aluminum Alloy 6063
Aluminum alloy 6063 is a medium strength aluminum alloy that is also known as an architectural alloy since it is used for intricate and complex designs. As with 6061, alloy 6063 has T4 and T6 tempered grades. Since 6063 is from the 6000 series of aluminum alloys, its major alloys are manganese and silicon where manganese increases the alloy’s strength while silicon lowers its melting point.
The composition of alloy 6063 makes it ideal for conditions where lightweight is a necessity and strength is required. The low density of alloy 6063 makes it easy to use to form complex shapes without adding weight, which is a factor that contributes to the wide use of 6063. Since 6063 does not have a copper content, it has higher resistance to corrosion. The weldability of 6063 is higher than that of other aluminum alloys.
Aluminum alloy 6063 is referred to as architectural aluminum due it being able to be soft anodized to produce an aesthetically pleasing colored finish for visually pleasing building applications. Part of the reason for the use of 6063 for architectural applications is due to its ability to endure harsh and severe weather conditions.
Aluminum Alloy 6082
Like aluminum alloy 6063, aluminum alloy 6082 is a medium strength aluminum alloy that is used for structural purposes due to its superior strength, which is higher than any of the other 6000 series alloys. The exceptional strength of alloy 6082 is due to the high amount of manganese, 0.4% up to 1%, that is added to 6082 that controls its grain structure. The increased strength of 6082 makes it possible for the alloy to withstand higher levels of stress, a characteristic that enhances its machinability.
Although alloy 6082 has high structural strength, it is not used for architectural or aesthetic purposes because it does not anodize well. It is still used for construction purposes such as scaffolding, bridges, transportation, and engineering applications. As with other 6000 series alloys, alloy 6082 has an O, T4, and T6 series that have been tempered.
The weldability, braze ability, corrosion resistance, formability, and machinability of alloy 6082 make it useful in several forms including rods, bar stock, and machining stock. Although it is a relatively new alloy, alloy 6082 has found wide use in its T6 form in the auto, aviation, and high-speed rail industries. The properties of aluminum alloy 6082 make it an excellent alloy for hot forging since it is capable of forming aluminum products with diverse dimensions. The products of alloy 6082 have excellent processing performance, corrosion resistance, do not deform after processing, are easy to coat, and have effective oxidation.
Aluminum Alloy 7075
Aluminum alloy 7075 is coveted as the highest strength alloy of all the aluminum alloys. Unlike 6000 series aluminum alloys, alloy 7075 has zinc, copper, and magnesium as alloying elements to create strength of 83,000 psi and resistance to stress corrosion cracking, which makes alloy 7075 an excellent material for use in high stress structural applications. Its forgings have superior static strength for use in airframe construction and stressed aircraft parts. The tempered series of alloy 7075 are T6, T651, T7351, and T76.
T6 alloy 7075 has the highest strength and lowest toughness and stress corrosion cracking resistance, which make it unusable for cryogenic applications. Alloy 7075-T73 has improved resistance to stress corrosion, improved exfoliation, but with decreased strength. The high strength, low density, thermal properties, and its ability to be polished has made alloy 7075 widely used in mold tooling.
Series 7000 aluminum alloys are very commonly used for transport applications due to their strength. Alloy 7075 was first used for the construction of a fighter jet, an aircraft that had excellent maneuverability due the high strength of 7075. Once the strength of alloy 7075 was discovered, it has been used for the production of rock-climbing gear, bicycle parts, skate frames, shafts for lacrosse sticks, and hang glider frames. For the military, alloy 7075 is used for the manufacture of the M16 rifle and AR-15 rifle.
The four aluminum alloys described above are a small sampling of the many aluminum alloys that are used for aluminum forging. The ones described are the most widely used and have the necessary properties and characteristics required for aluminum forging, such as strength, durability, corrosion resistance, toughness, and ductility.
Types and Mechanical Properties of Forgeable Aluminum Alloys Key - ◎ Excellent - 🞅 Good - △ Fair - 🞩 Poor
Desired Properties
Material
Si Content (MASS%)
Mechanical Properties
Forgeability
Former Sumitomo Designation
Temper
Tensile Strength (N/mm)²
Proof Stress (N/mm)²
Elongation (%)
High Strength
6061
T6
315
275
19
◎
SG210
T6
400
360
18
◎
GS310
T6
390
345
18
◎
2011
T8
410
315
15
◎
2014
T6
480
275
22
◎
2017
T4
440
275
22
◎
Abrasion Resistance
4032
T6
12
380
315
9
🞅
SC100
T6
10
440
390
8
🞅
SC300
T6
10
480
420
8
🞅
SC150
T6
15
420
390
2
△
High-Temperature Strength
2618
T6
440
370
10
◎
CG29
T6
520
400
14
◎
Chapter 4: The Benefits of Aluminum Forging
Forging is a very old and traditional method of metal working that has been used for centuries to form weapons of war, cutlery, cookware, jewelry, and structural supports. The original method of forging was to beat a metal into submission using an anvil, hammer, and heat. The process in the modern era is technologically advanced but uses some of the same basic processes of its ancestors.
Surface Finish
One of the most notable factors related to the use of aluminum for the production of components is aluminum’s smooth, even, and appealing finish, which resembles polished silver. Although the forging process produces products with this characteristic finish, it also creates a wide range of surfaces including ones with sharp serrations and jagged peaks, which may require further finishing or be a part of a product’s purpose and use.
Design Flexibility
The results of aluminum forging rely on the design and configuration of the die being used to produce a product. Aluminum design engineers use the parameters provided by clients to create dies with the dimensions and configurations for the products to be forged. The limitations to the process are the manufacturability of the design. The use of computer aided design (CAD) makes it possible to pretest a design prior to production.
Strength
Aluminum forging produces components, parts, products, and instruments that are stronger than those produced by casting and machining. During the forging process, the grain structure of a shaped component follows the shape of the component, which improves the strength of the component and enhances its durability. Forged aluminum is used for applications that require a component to endure repetitive loading, frequent impact, and stressful conditions due to aluminums impact resistance and strength.
Cost
When all the factors of a manufacturing process are equal, such as material cost, lead times, and other factors, aluminum forging is less expensive. The tooling for aluminum forging is far less costly than tooling for aluminum die casting and has a higher production rate.
Mechanical Properties
The alteration of the microstructure of aluminum alloys during forging improves their mechanical properties and gives them increased tensile strength, yield strength, toughness, and resistance to fatigue.
Durability and Reliability
One of the difficulties with other aluminum forming processes is the porosity and voids that are present in the final products, which limit the performance of certain products. The compressive forces of the aluminum forging process eliminates voids and porosity increasing the durability, performance, and reliability of aluminum products.
Dimensional Accuracy
Shrinkage is not a factor with aluminum forging since the metal is heated to just below or just above its recrystallization point. The billet or workpiece is processed in a solid form to provide dimensional accuracy and integrity.
Property Reliability
A major factor in the choice of aluminum forging is the retention of aluminums exceptional properties. Although the metal is shaped, manipulated, and deformed, none of the forging actions removes any of aluminums positive properties.
Material Waste
A drive factor in modern manufacturing is the elimination and limiting of waste, which can be damaging and costly. The flash produced from open and closed die forging can easily be reused and recycled, negating any potential waste. Aluminum is one of the most recycled materials on earth and can be used innumerable times.
High Volume Production
Aluminum forging is capable of rapidly producing thousands of complex and intricate shapes in a short amount of time. The time from initial introduction of a design to the delivery of a finished product can be as little as two months or less. Although many thousands of pieces may be produced, aluminum forging produces minimal waste.
Conclusion
Aluminum forging is a process that places aluminum alloys under pressure to form high strength, durable parts. The process of aluminum forging involves pressing, pounding, and squeezing an aluminum billet under great pressure to create parts that have high strength.
The choice of the forging process for aluminum is to ensure that components have all of the positive properties of aluminum where weight and mass must be minimized and reliability is a necessity.
In general, forging is used to form metals that have been heated to just above their recrystallization temperature and metals that are shaped at room temperature, which are the distinctions between hot and cold forging.
It must be understood that not all aluminums can be used for forging, which necessitates careful selection of the type of aluminum to be used for a project.
In the 170 years since its introduction, aluminum alloys have become the most widely used industrial metal with several million tons of it being used every year including new and recycled aluminum.
Leading Manufacturers and Suppliers
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