Effect of Bake Hardening Treatment on Mechanical Properties of 7075 Aluminum Alloy Sheets Fabricated by Twin Roll Strip Casting

The effect of age hardening and bake hardening treatment on the mechanical properties of 7075 aluminum alloy sheets fabricated by twin roll strip casting (TRC) was studied. The hardness of the TRC 7075 sheets was continuously increased by natural aging up to 96 h and the highest yield strength at that condition was about 308 MPa. When the natural aged sample was bake-hardened at 180 degrees C for 30 min, the yield strength was 304 MPa, which indicated that the bake-hardening treatment did not increase the strength. The result suggests that the temperature was too high to produce the optimum amount of fine precipitates which result from coarsening of the eta'-phase. To improve the paint-bake hardening properties without the loss of elongation, pre-aging treatment before natural aging was additionally applied at 120 degrees C for 30 min, and then the yield strength after the bake-hardening treatment was increased to 432 MPa.