During our March 19, 2015 metallurgy question and answer webinar I answered the following question: What is needed to meet specs for solution treated and aged 7175 aluminum? This video recording shows my reply.
Whether you are through hardening steel, annealing a cold-worked metal, or solution treating an aluminum alloy, the heat treating temperature is critical for obtaining the desired microstructure, and therefore, the desired metal properties. Using a temperature that is too hot can result in a metallurgical transformation that proceeds too quickly or the formation of undesired phases. Using a temperature that is too low can result in incomplete metallurgical transformations, cold worked metals that do not soften sufficiently, or insufficient stress relief.
Rockwell and Brinell hardness tests are common metal characterization methods used to determine whether metal stock or a metal component has the required properties. The reason for this is that these tests are simple and quick to perform, in addition to being inexpensive. However, while these tests do provide useful information, there is a danger to the common practice of specifying only hardness and alloy composition on component design drawings.
The strength of metals is improved by impeding the motion of dislocations through the metals. One approach to achieving this improvement is to form a uniform distribution of closely spaced sub-micron sized particles throughout an alloy. The particles, called precipitates, impede dislocation motion through the alloy. Not every alloy can be precipitation strengthened. Alloys that can be precipitation strengthened include Al-Cu, Al-Mg-Si, Cu-Be, and 17-8 PH steel.