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The microstructure and creep characteristics of cast Mg-3Si and Mg-3Si-1Gd alloys

机译：Mg-3Si和Mg-3Si-1Gd铸造合金的组织和蠕变特性

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摘要

The effect of 1 wt% Gd addition on the creep behavior of a cast Mg-3Si alloy was investigated by impression creep testing in the temperature range of 448-523 K under punching stresses in the range of 175-450 MPa for dwell times up to 4200 s. It was found that the creep strength of the Mg-3Si base alloy was improved by Gd addition. This was attributed to the modification of the primary Mg_2Si particles, solid solution strengthening of Gd in the Mg matrix, and the formation of a new intermetallic phase with a composition close to Mg_3Si_2Gd_2. Creep behavior of the binary Mg-3Si alloy can be divided into the low-and high-stress regimes, with the respective stress exponent values in the range of 5.1-6.0 and 8.8-11.5 and average activation energies of about 81 kJ mol~(-1) and 124.5 kJ mol~(-1). The creep behavior of the ternary Gd-containing alloy, however, was expressed by a single linear relationship over the whole stress and temperature ranges studied, with stress exponents in the range of 8.2-8.5 and an average activation energy of 111.1 kJ mol~(-1). The creep activation energies were all stress dependent, and thus in the binary alloy, stress-assisted climb of dislocations, controlled by pipe and lattice diffusion were the dominant creep mechanisms in the low- and high-stress regimes, respectively. In the ternary Gd-containing alloy, power law creep is valid and it can be suggested that the operative creep mechanism is dislocation climb controlled by lattice diffusion.
机译：通过在175-450 MPa的冲切应力下，在448-523 K的温度范围内进行压痕蠕变试验，研究了1wt％的Gd对铸造Mg-3Si合金蠕变行为的影响，停留时间长达175-450 MPa。 4200秒发现通过添加Gd可以改善Mg-3Si基合金的蠕变强度。这归因于原始Mg_2Si颗粒的改性，Mg基质中Gd的固溶强化以及新的金属间相的形成，其组成接近Mg_3Si_2Gd_2。二元Mg-3Si合金的蠕变行为可分为低应力和高应力两种，其应力指数值分别在5.1-6.0和8.8-11.5之间，平均活化能约为81 kJ mol〜（ -1）和124.5 kJ mol〜（-1）。然而，在研究的整个应力和温度范围内，含三元Gd合金的蠕变行为均表现为单线性关系，应力指数在8.2-8.5范围内，平均活化能为111.1 kJ mol〜（ -1）。蠕变激活能全都与应力有关，因此在二元合金中，由管和晶格扩散控制的位错应力辅助爬升分别是低应力和高应力状态下的主要蠕变机制。在含三元Gd的合金中，幂律蠕变是有效的，可以认为有效蠕变机理是由晶格扩散控制的位错爬升。

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