Effect of three-step homogenization on microstructure and properties of 7N01 aluminum alloys

The effect of different homogenization treatments on the microstructure and properties of the 7N01 aluminum alloy was investigated using hardness measurements, electrical conductivity measurements, tensile and slow strain rate tests, electron probe microanalysis, optical microscopy, scanning electron microscopy, and transmission electron microscopy. The results revealed that three-step homogenization improved the uniformity of Zr distribution by eliminating segregation of the main alloying elements. During the second homogenization step at 350 °C for 10 h, coarse and strip-like equilibrium η phases formed which assisted the nucleation of Al3Zr dispersoids and reduced the width of the precipitate-free zone of A13Zr dispersoids. As a result, coarse recrystallization was greatly reduced after homogenization at 200 °C, 2 h ＋ 350 °C, 10 h ＋ 470 °C, 12 h, which contributed to improving the overall properties of the 7N01 aluminum alloys.

Microstructure,mechanical properties and stress corrosion behavior of friction stir welded joint of Al-Mg-Si alloy extrusion

Microstructure,mechanical properties and stress corrosion behavior of friction stir welded(FSWed) AlMg-Si alloy were investigated.The average grain sizes of shoulder-affected zone(SAZ),nugget zone(NZ),heat-affected zone(HAZ) and base material(BM) are 6.03,4.80,168.30 and 127.24 μm,respectively.The thermo-mechanically affected zone(TMAZ),which is generated on the edge position between HAZ and weld nugget zone,has a narrow width of 400 μm.The ultimate tensile strength(UTS) of FSWed joint is 232.20 MPa,about 91.04% with respect to that of base material of 255.06 MPa,and the joint fracture occurs at HAZ on advancing side(AS).The FSWed joint is more susceptive to stress corrosion cracking(SCC) than base material,and the SCC susceptibility increases with the rise in temperature.The residual UTS of FSWed joints in constant loaded tests at the load levels of90,105 and 120 MPa is 89.97%,67.50% and 54.75% of the UST of FSWed joint in air,respectively.The increase of the load in constant loaded tests and four-point beambent tests accelerates the SCC of FSWed joints.