Below is a list of Aluminum Heat Treating manufacturers from LONDONDERRY, New Hampshire. Aluminum heat treating is a process that is used to harden or soften aluminum by heating or cooling it until the desired level of hardness is reached. Heat treating is an energy-intensive process. In aluminum, the structure and composition of the grains determines the overall mechanical qualities of the metal. This internal atomic structure changes when it is heated; this in turn changes the metal’s mechanical behavior.