| AZ31 magnesium alloy, as one of the most famous wrought alloys, was widely used in aerospace, automobile and 3C fields because of excellent strength, plasticity and multiple mechanical properties. Nevertheless, the researches on anti-corrosion and elevated-temperature mechanical properties of AZ31 were limited. To improve its anti-corrosion and heat-resistance, this paper was investigated on the microstructure, corrosion and elevated-temperature mechanical properties of AZ31 additions Sr and Y.AZ31-xSr and AZ31-0.5Sr-xY magnesium alloys were prepared using "Incorporation Method". The LSV and immersion test were carried out in 3.5% NaCl netural solution. The elevated-temperature mechanical properties of AZ31-xSr and AZ31-0.5Sr-xY magnesium alloys, as well as the flow stress behavior of AZ31-0.5Sr-1.5Y in hot-compress were studied systematically using Gleeble-1500 D thermo mechanical simulator. Meanwhile, the analyses on microstructure, composition and phases were studied using OM, SEM, EDS and XRD. The results were shown as:1 The grain of AZ31 independent addition Sr was refined, especially with addition 0.9wt% Sr, and theβ-Mg17Al12 phase transformed from continuous network to scattered form. Simultaneously, the Al4Sr phase, distributed along the boundaries of crystals, was formed in AZ31-xSr magnesium alloys.2 The grain was further refined and the amount ofβ-Mg17Al12 decreased sharply in AZ31 with multiple additions 0.5%Sr+xY. What's more, the dendrite was formed and the acicular and bar phases were distributed along secondary dendrite. It's showed that the grain refinement was obvious in AZ31-0.5Sr-1.5Y, and that the Al2Y, Al3Y phases were distributed both in intracrystalline and along grain boundaries.3 The corrosion behaviors of AZ31-xSr and AZ31-0.5Sr-xY in 3.5% NaCl neutral solution were studied using Tafel polarization curve and statistic weight losing methods. It's indicated that the corrosion resistance of AZ31 was improved slightly with independent addition Sr, while improved apparently with multiple additions 0.5%Sr+xY. With the smallest corrosion current density and corrosion rate, the corrosion resistance of AZ31-0.5Sr-1.5Y magnesium alloy was proved to be best in the research.4 The relationship between microstructure and corrosion properties showed that the grain AZ31 was refined with independent Sr addition, and that the improvement of corrosion resistance of AZ31 lied on the content of Sr, the amount and distribution of secondary phases. The fact that the anti-corrosion of AZ31 with multiple addition Sr and Y was further improved was due to:①Rare earth element Y had a high solid solubility in Mg;②The effective area ratio (Ac/Aa) of micro-galvanic declined because the amount ofβ-Mg17Al12 phase reduced and transformed from network to scattered form;③The morphology and distribution of rare earth phases made the micro-galvanic corrosion between grains and crystal boundaries more dispersed.5 The results of static tensile test at 250℃showed that AZ31 with addition appropriate amount of Sr and Y performed good mechanical properties, with Ultimate Tensile Strength increasing by 54.56% and elongation 53.02%. It's owing to:①obvious grain refinement in AZ31 with addition Sr and Y;②reduction ofβ-Mg17Al12 brittle phase;③disperse reinforcement of precipitation phase with highly thermal stability.6 The research on the flow stressσof AZ31-0.5Sr-1.5Y at T=250~450℃,ε&=0.01~1s-1 indicated thatσdecreased with increasing temperature, and increased with increasing strain rate. It should be noted that the steady state deformation occurred at T=450℃,ε& =0.01s-1. Moreover, the relationship betweenσand T andε& followed a power function, and the calculating formula ofσusing parameter Z could be expressed as:(?)Where,Ζ=ε&exp(Q RT). The relative mistake between measured stress and predicted stress is below 3.5%, and the predicted stress could be as the theoretical preferences forε& in hot processing.
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