1975 Heat Treated Alloy Sheet Research And Organizational Performance

The effects of solution and aging on the microstructure and properties of1975aluminum alloy sheet were studied by tensile tests, hardness, electric conductivity measurement, X-ray diffraction (XRD), Scanning electronic microscopy analysis and transmission electron microscopy (TEM). On this basis, corrosion properties of1975aluminum alloy sheet were studied and the microstructure and properties of the Al-Zn-Mg alloy containing Sc, Zr (1975alloy) and Al-Zn-Mg alloy without Sc, Zr welded joint were studied. The results are as follows:(1) The appropriate heat-treatment regime of1975aluminum alloy sheet is solution treated at470℃for1h, aged at120℃for24h. Under this condition, the mechanical properties σb, σ0.2,δ5, HB and electric conductivity can reach532MPa、496MPa、15.07%、176HB and34.3%(IACS) respectively.(2) In solution treatment process, the T-phase gradually dissolves in solid solution. There is still small amount of residual containing Fe, Mn, Si impurity phase in the solid solution matrix. During aging, the supersaturated solid solution decompose and separate out η’and η. With the aging temperature rising or aging time longer, precipitation of the phase η’coarse grain boundary intermittent coarse η phase and PFZ. The high strength of this alloy is from subgrain strengthening caused by Al3(Sc, Zr) particles and precipitation strengthening caused by η’.(3) After aging, the sensitivity variation for intergranular corrosion, exfoliation corrosion and stress corrosion of1975aluminum alloy is as follows:under aging (120℃/12h)>peak aging(120℃/24h)>over aging (120℃/36h). Corrosion sensibility of alloy is related to the characteristics of equilibrium phase η and precipitated free zone (PFZ). When the grain-boundary equilibrium phases have more discontinuous distribution, larger size and the PFZ is wider,the corrosion sensibility is lower. On the contrary, when the grain-boundary equilibrium phases have chain distribution and smaller size, the corrosion sensibility is higher.(4)1571Wire has a good compatibility with Al-Zn-Mg and1975base alloy. Using MIG welding technology, three alloy sheet mechanical properties of welded joints can reach the following:Al-Zn-Mg alloy: σb=398MPa, σ0.2=253MPa,δ5=8.7%, the welding coefficient is0.803;1975alloy:ab=405MPa, σ0.2=306MPa, δ5=6.3%and the welding coefficient is0.766.(5) The weld joint of Al-Zn-Mg and the1975aluminum alloy plate was composed of weld seam zone, semi fusion zone, heat-affection zone and base-material zone. The heat-affection zone could be divided into two zones, quenching zone and overaged zone. Welded joints fracture mostly occurred in the low strength of the overaged zone. The high strength of welded joints come from Al3(Sc, Zr) caused by dispersion strengthening. Trace Sc and Zr can inhibit the heat-affected zone recrystallization and increase the intensity of the heat affected zone.