Research on quench sensitivity of B93 aluminum alloy for large sized bars

The quench sensitivity of the Al-Zn-Mg-Cu alloy for large sized bars were studied by means of hardness test, X-ray diffraction analysis, finite element simulation and microstructure observation. The results show that, the closer to the centre of the quenching bars, the larger quantities of equilibrium MgZn(2) are observed in the grain inner and on the grain boundary and keep growing up. And small quantity of hardening precipitates are exhibited in the 120 degree C/24 h aging samples. It results in the decline of the age-hardening effect. For the surface of the bar, the second phase was not observed and the homogeneous content in the grain inner was obtained, which may attribute to the super saturated solid solution. A number of eta ' dispersoid were found at the surface. The dispersive phases are able to promote the precipitation strengthening effect and the hardness of the alloy reach the peak. The value of the quenching depth is 30 mm, and the critical quench cooling rate is 15 degree C/s.