The effects of
progressive solution treatment on
microstructure and mechanical properties of 7A04 aluminum alloy were investigated.
Results indicate that after solutionized under condition of 470 ℃, 5 min+485 ℃, 9 min and subsequent aging process of 140 ℃, 6 h+150 ℃, 1 h, σ_b, σ_(0.2) and δ_5 of 7A04 alloy reach 544.6 MPa, 498.8 MPa and 11.1% respectively. Metallography observation indicates that the grain size after short-time
progressive solution treatment(470 ℃, 5 min+485 ℃, 39 min) is smaller than that after single-stage solution at 485 ℃. SEM observation indicates that the progressively solutionized sample in tension test behaves as typical dimpled fracture. X-ray diffraction analysis indicates that after progressive solution under the condition of 470 ℃, 5 min+485 ℃, 9 min, MgZn_2 as main strengthening phase is totally dissolved except a small amount of Al_2Cu. EDAX analysis indicates that the main undissolved phases are inclusions rich in Fe and Cu. Because the grain size of the sample progressively solutionized at 470 ℃, 5 min+485 ℃, 9 min is smaller than that of single-step solutionized at 485 ℃, the supersaturation degree of the progressivly solutionized sample reaches that of the sample single-step solutionized at 500 ℃, 20 min, and obtains the highest mechanical properties after subsequent aging, which is equal to those got by traditional solution process.