Li Chengbo

Effect of homogenization time on quench sensitivity of 7085 aluminum alloy

The effect of homogenization time on quench sensitivity of a cast 7085 aluminum alloy was investigated by means of end-quenching test, optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that with the increase of homogenization time from 48 h to 384 h, quench sensitivity increased slightly as the largest difference in the hardness was increased from 5.2% to 6.9% in the end-quenched and aged specimens. Prolonging homogenization had little effect on the grain structure, but improved the dissolution of soluble T phase and resulted in larger Al3Zr dispersoids with a low number density. Some small quench-induced η phase particles on Al3Zr dispersoids were observed inside grains during slow quenching, which decreased hardness after subsequent aging. The change in the character of Al3Zr dispersoids exerted slight influence on quench sensitivity.

Grain structure effect on quench sensitivity of Al—Zn—Mg—Cu—Cr alloy

Abstract The effect of grain structure on quench sensitivity of an Al—Zn—Mg—Cu—Cr alloy was investigated by hardness testing, optical microscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and scanning transmission electron microscopy. The results show that with the decrease of quenching rate from 960 °C/s to 2 °C/s, the hardness after aging is decreased by about 33% for the homogenized and solution heat treated alloy (H-alloy) with large equiaxed grains and about 43% for the extruded and solution heat treated alloy (E-alloy) with elongated grains and subgrains. Cr-containing dispersoids make contribution to about 33% decrement in hardness of the H-alloy due to slow quenching; while in the E-alloy, the amount of (sub) grain boundaries is increased by about one order of magnitude, which leads to a further 10% decrement in hardness due to slow quenching and therefore higher quench sensitivity.