Effects of Quench Rate on Mechanical Properties and Microstructures of High-Strength 7046A Aluminum Alloy

The Jominy end-quench (JEQ) test was adopted to investigate the quench sensitivity of Al-6.6Zn-1.8Mg-0.23Cu-0.22Mn-0.21Zr (7046A) alloy. The mechanical properties of the aged alloy were studied by means of a hardness and tensile property test, whereas microstructure observation was realized by x-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show the following: (I) inhomogeneity exists in the mechanical properties of as-aged alloy and they generally decrease with the distance from the quenched end of the bar (D) where the depth of losing 10% of maximum hardness is 196mm. (II) Average cooling rates decreased with the increase of D. When the critical average cooling rate is about 1Ks(-1), 90% of the maximum hardness can be obtained. (III) On the other hand, the influence of Al3Zr dispersoids and Al6Mn dispersoids on the precipitate behavior of MgZn2 was studied, indicating that Al3Zr and Al6Mn were effective heterogeneous precipitates sites in the slow quenching process.