We often state that there are only two groups of aluminum alloys that are heat treatable. In fact, all of the aluminum alloys can be heat treated by annealing and/or stress relieving. This will embrace the so-called “non-heat-treatable alloys” such as 1xxx, 3xxx, 4xxx and 5xxx. These heat-treatment procedures are simply non-strengthening treatments. The only way to strengthen these alloys is by work-hardening.
On the other hand, the following alloys can be successfully thermally strengthened, which will alter the mechanical properties and the alloy microstructure. This applies to the following alloys: 2xxx, 6xxx and 7xxx.
The procedure of thermally strengthening aluminum alloys is very similar in principle to the thermal strengthening of the precipitation-hardening stainless steels. However, the process temperatures for aluminum are considerably lower than for steel heat treatment.
The necessity for temperature accuracy and temperature uniformity is MANDATORY for aluminum and its heat treatment. Next time, we will look at the specific thermal processes for aluminum.