Effects of quenching methods on shape memory properties of Cu-28Zn-3Al wt. % alloy produced by gravity casting

Abstract

In recent years, Cu-Zn-Al alloys are studied intensively due to their excellence in shape memory effect (SME), good mechanical properties, along with accessible production process and cost. Cu-Zn-Al Shape Memory Alloy easily form stabilization in martensite phase that leads to SME properties reduction, but can be minimized by applying alternative quenching methods. In this research, several quenching methods are proposed to minimize the phase stabilization of martensite. The Cu-28Zn-3Al alloy was produced by gravity casting and homogenized at 800 ℃ for 2h followed by air cooling. Furthermore, as-homogenized plate was betatized at 850 ℃ for 30 minutes and then subsequently quenched using three different methods: direct quench (DQ), up quench (UQ), and step quench (SQ). Morphology, phase transformation, hardness, and strain recovery characterization are examined using an optical microscope, SEM-EDS, XRD, DSC, Vickers, and bending tests. The results showed that the DQ and UQ samples consist of V-shape βˈ[M18R] martensite as a matrix and retained α[A1] as the second phase. The volume fraction ratio of βˈ[M18R]: α[A1] is (98.4:1.6) and (92.9:6.1) for DQ and UQ, respectively. However, the SQ sample did not indicate the presence of the martensite phase and did not show any recovery rate. Bending test showed that DQ and UQ had 27.2% and 36.3% of recovery rate, respectively.