Assessment of the mechanical behaviour of thermally aged B and Fe modified CuZnAl shape memory alloys

Abstract

The mechanical properties of unmodified, and 0.05 wt.% B and Fe modified CuZnAl alloys produced following liquid metallurgy route was investigated. The alloys were subjected to thermal ageing treatments at 200 °C and 450 oC; while mechanical testing and light microscopy were used for assessing the alloy response to the treatment. The results show that Microstructures with different structural features were observed in the unmodified-, and B, Fe modified- Cu-Zn-Al alloys, both in the unaged and aged conditions. The hardness of the unmodified Cu-Zn-Al alloy and the B modified Cu-Zn-Al alloys increased significantly with ageing at 200 °C and 450 °C, while the Fe modified Cu-Zn-Al alloy only exhibited marginal changes in hardness with thermal ageing treatment. Also, the ultimate tensile strength of the unmodified CuZnAl alloy was the most sensitive to ageing treatment performed at 200 °C, as UTS increase as high as 18.5% was compared to the 6.8 and 6.1% increases obtained for the Fe and B modified CuZnAl alloy compositions. The percent elongation of all the CuZnAl alloy compositions improved significantly with ageing treatment with peak values obtained when ageing is performed at 200 °C. It was opined that the generally marginal changes in the mechanical properties of the modified CuZnAl alloy compositions on ageing was due to the stabilizing effect of the B and Fe modifiers on the CuZn primary phase, which curtailed to some extent the tendency for precipitation of secondary phases.