Not sure I understand the question, but I will give it a try.

There are essentially two families of aluminum alloys, the heat treatable and the nonheat treatable.

The heat treatable aluminum alloys are strengthened by a heat treatment that involves heating the alloy to a "high" temperature  to alloy the alloying constituents to go into solution with the aluminum. The alloy is then quenched to produce a supersaturated solution of the aluminum and the alloying elements. The alloy is then aged, either artificially or naturally. Artificial aging involves heating the alloy to a "low" temperature which causes the super saturated elements to clump within the atomic lattice. Any mechanism that strains the lattice results in hardening and strengthening the metal.

The nonheat treatable aluminum alloys are strain hardening by cold working the alloy system. The strain hardening is accomplished by rolling the alloy by cold rolling or stretching the alloy.

Both alloy systems loose strength when they are welded. The heat treatable alloys overage when welded. Overaging, i.e., holding the  alloy at a higher temperature than the aging process, allows the alloying constituents to precipitate to the grain boundaries, thereby reducing the strength in the as-welded condition.

the strain hardened

Not sure I understand the question, but I will give it a try.

There are essentially two families of aluminum alloys, the heat treatable and the nonheat treatable.

The heat treatable aluminum alloys are strengthened by a heat treatment that involves heating the alloy to a "high" temperature  to alloy the alloying constituents to go into solution with the aluminum. The alloy is then quenched to produce a supersaturated solution of the aluminum and the alloying elements. The alloy is then aged, either artificially or naturally. Artificial aging involves heating the alloy to a "low" temperature which causes the super saturated elements to clump within the atomic lattice. Any mechanism that strains the lattice results in hardening and strengthening the metal.

The nonheat treatable aluminum alloys are strain hardening by cold working the alloy system. The strain hardening is accomplished by rolling the alloy by cold rolling or stretching the alloy.

Both alloy systems loose strength when they are welded. The heat treatable alloys overage when welded. Overaging, i.e., holding the  alloy at a higher temperature than the aging process, allows the alloying constituents in the HAZ to precipitate to the grain boundaries, thereby reducing the strength in the as-welded condition.

The strain hardened alloys are "annealed" when welded. That is the benefits of strain hardening are lost in the HAZ when held at temperature during the welding process.

The degree of degradation is dependent on the particular alloy, the hardening mechanism employed, and the time at temperature. As it turns out, 6061-T6, a popular aluminum alloy is also a heat treatable alloy. when it is welded, it looses about 40% of its tensile strength and about 50% of its yield strength.

Both the heat treatable and the nonheat treatable alloys can be strengthened to different degrees, as indicated by the "T" number of the heat treatables or by the "H" numbers of the strain hardenable alloys.

The "T" numbers indicate the degree of cold work, i.e., reduction in cross section. The "H" numbers indicated the amount of hardening. 

I hope that is what you are looking for.

Al