Grain structure effect on quench sensitivity of Al-Zn-Mg-Cu-Cr alloy
(1. School of Materials Science and Engineering, Central South University, Changsha 410083, China;
2. Key Laboratory of Nonferrous Metal Materials Science and Engineering, Ministry of Education,
Central South University, Changsha 410083, China;
3. Light Alloy Research Institute, Central South University, Changsha 410083, China;
4. Nonferrous Metal Oriented Advanced Structural Materials and
Manufacturing Cooperative Innovation Center, Central South University, Changsha 410083, China)
2. Key Laboratory of Nonferrous Metal Materials Science and Engineering, Ministry of Education,
Central South University, Changsha 410083, China;
3. Light Alloy Research Institute, Central South University, Changsha 410083, China;
4. Nonferrous Metal Oriented Advanced Structural Materials and
Manufacturing Cooperative Innovation Center, Central South University, Changsha 410083, China)
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.
Key words: grain structure; Al-Zn-Mg-Cu-Cr alloy; dispersoids; quench sensitivity