Abstract:

This article aims to explore the age hardening responses of both as-extruded and as-aged Mg-2.5Sn-1.5Ca-xAl alloys (x = 2.0, 4.0 and 9.0 wt%, termed TXA322, TXA324 and TXA329, respectively) through microstructural and mechanical characterization. Results indicate that grain size of as-extruded TXA322, TXA324 and TXA329 alloys were ～ 16 μm, ～ 10 μm and ～ 12 μm, respectively. A number of <a> and <c+a> dislocations were observed in all the as-extruded samples. Guinier - Preston (GP) zones were evidently identified in TXA322 alloy, while only a small number of Mg₁₇Al₁₂ phases existed in both TXA324 and TXA329 alloys. An aging treatment facilitated the precipitation of a high number density of GP zones within the matrix of TXA322 alloy. In contrast, no obvious nano-precipitates were in as-aged TXA324 alloy. Numerous nano-Mg17Al12 phases were formed through a following aging treatment in TXA329 alloy. In terms of mechanical properties, it is apparent that an increment in ultimate tensile strength of ～ 46 MPa and ～ 40 MPa was yielded in peak-aged TXA322 and TXA329 alloys, while no obvious variations in UTS were present in peak-aged TXA324 alloy, in comparison with the as-extruded counterparts.

Key words: Magnesium alloys, Age hardening, Precipitations, Dislocations, Mechanical properties