Effects of Mg content on microstructure and mechanical properties oflow Zn-containing Al-xMg-3Zn-1Cu cast alloys
(National Engineering Research Center of Light Alloy Net Forming and State Key Laboratory ofMetal Matrix Composites, School of Materials Science and Engineering,Shanghai Jiao Tong University, Shanghai 200240, China)
Abstract: Effects of Mg content on the microstructure and mechanical properties of low Zn-containing Al-xMg- 3Zn-1Cu cast alloys (x=3-5, wt.%) were investigated. As Mg content increased in the as-cast alloys, the grains were refined due to enhanced growth restriction, and the formation of η-Mg(AlZnCu)2 and S-Al2CuMg phases was inhibited while the formation of T-Mg32(AlZnCu)49 phase was promoted when Mg content exceeded 4 wt.%. The increase of Mg content encumbered the solution kinetics by increasing the size of eutectic phase but accelerated and enhanced the age-hardening through expediting precipitation kinetics and elevating the number density of the precipitates. As Mg content increased, the yield strength and tensile strength of the as-cast, solution-treated and peak-aged alloys were severally improved, while the elongation of the alloys decreased. The tensile strength and elongation of the peak-aged Al-5Mg-3Zn-1Cu alloy exceed 500 MPa and 5%, respectively. Precipitation strengthening implemented by T′ precipitates is the predominant strengthening mechanism in the peak-aged alloys and is enhanced by increasing Mg content.
Key words: Mg content; low Zn-containing Al-xMg-3Zn-1Cu cast alloys; microstructure; aging response; strengthening mechanism