【作者】 苏再军；

【导师】 曾苏民； 刘楚明；

【作者基本信息】 中南大学 ， 材料科学与工程， 2013， 博士

【摘要】 摘要：Mg-Nd系铸造合金拥有优异的力学性能、高温抗蠕变性能及铸造性能,在航空、汽车、电子等领域中得到广泛的应用。Y元素具有比Nd更好的固溶强化和析出强化效果；Zn元素价格低廉,且添加少量Zn元素可产生较强的固溶强化和时效强化效果。目前,在Mg-Nd合金中添加Y和Zn对其组织及力学性能的影响尚未被系统研究。因此,本文以Mg-Nd合金为基体,通过加入不同含量的Y(0-6.0wt.%)和Zn(0.2-1.5wwt.%),深入研究铸造Mg-Y-Nd-Zn-Zr合金的显微组织、力学性能及强化机制,得出了如下研究结论：铸态Mg-2.4Nd-0.2Zn-0.5Zr合金主要由a-Mg、Mg12Nd相组成；增加Y的含量到2.5wt.%时,合金中出现了Mg24Y5相。与Mg-4.2Y-2.4Nd-0.2Zn-0.5Zr合金相比,在Mg-4.2Y-2.4Nd-0.5Zr合金中加入(0.5-1.5)Zn后,合金中出现Mg12YZn相。固溶处理后,Mg-Y-Nd-Zn-Zr合金中的Mg12Nd相和Mg24Y5相基本消失。225℃峰时效态Mg-Y-Nd-Zn-Zr合金主要的析出相为β’相。β’相的体积分数随Y的增加随之增加,随Zn的增加先升高后降低。在250℃时效时,Mg-6.0Y-2.4Nd-0.2Zn-0.5Zr合金的脱溶序列为：α-Mg(S.S.S.S)→β"→β’→β1→β。在室温下,峰时效态Mg-Y-Nd-Zn-Zr合金的屈服强度随Y的增加逐渐提高,随Zn的增加先升高后降低。Mg-4.2Y-2.4Nd-0.2Zn-0.5Zr合金的抗拉强度、屈服强度和伸长率分别为330MPa、265MPa和5.8%; Mg-6.0Y-2.4Nd-0.2Zn-0.5Zr合金在250℃高温拉伸的抗拉强度、屈服强度、伸长率分别为280MPa.235MPa、11.0%。合金优异的力学性能归因于沿棱柱面分布、具有较大体积分数及纵横比的片状β’相。对铸态Mg-Y-Nd-Zn-Zr合金屈服强度起主要作用的是第二相强化；在固溶态、时效态下,固溶强化、时效析出强化分别对合金屈服强度的贡献最大。更多还原

【Abstract】 Abstract:Mg-Nd alloys are very attractive for aerospace, racing automotive and electronics industries because of their excellent mechanical properties, thermal stability and casting performance. Y element has significant strengthening effect on magnesium alloys than Nd. Zn is one of the cheap alloy elements, and the magnesium alloys containing trace amount of it possess excellent solid solution strengthening and age hardening effect. At present, the effects of adding Y and Zn element in Mg-Nd alloys on microstructure and mechanical properties have not been systematic researched. Therefore, in this article, based on the Mg-Nd alloys, the new type of Mg-Y-Nd-Zn-Zr alloys are designed by adding Y(0-6.0wt.%) and Zn(0.2-1.5wt.%) element content, the microstructure、mechanical properties and strengthening mechanisms of Mg-Y-Nd-Zn-Zr alloys were investigated deeply and systematically. The main conclusions can be summarized as follows:As cast Mg-2.4Nd-0.2Zn-0.5Zr alloy are composed mainly of a-Mg, Mg12Nd phases. Mg24Y5phase appear in Mg-2.5Y-2.4Nd-0.2Zn-0.5Zr alloys with increasing Y content. Mg-4.2Y-2.4Nd-0.5Zr-(0.5-1.5)Zn alloys contains Mg12YZn phase besides that in Mg-4.2Y-2.4Nd-0.2Zn-0.5Zr alloy. After solution treatment, Mgi2Nd and Mg24Y5phases in Mg-Y-Nd-Zn-Zr alloys almost disappear.In225℃peak-aged condition, the main precipitate phases of Mg-Y-Nd-Zn-Zr alloys are β’ phase. With increasing Y content, the volume fraction of β’ phase increase; with increasing Zn content, the volume fraction of β’ phase first increase then decrease. The precipitation sequence of Mg-6.0Y-2.4Nd-0.2Zn-0.5Zr alloy is:a-Mg (S.S.S.S)→β"→β’→β1→β during ageing at250℃.At room temperature, the yield strength of the peak-aged Mg-Y-Nd-Zn-Zr alloys increase with increasing Y content; the yield strength of alloys first increase then decrease with increasing Zn content. Mg-4.2Y-2.4Nd-0.2Zn-0.5Zr alloy exhibits the optimal mechanical strength, the value of ultimate tensile strength (UTS), yield strength (YS) and elongation (ε) are330MPa,265MPa and5.8%, respectively. The Mg-6.0Y-2.4Nd-0.2Zn-0.5Zr alloy exhibits the optimal mechanical strength, with UTS of280MPa, YS of235MPa and s of11.0%at250℃tensile temperature. The high mechanical properties of Mg-Y-Nd-Zn-Zr alloys are mainly attributed to the high volume fraction, the prismatic β’ precipitate of big aspect ratio.The secondary phase strengthening dominates the strengthening of as cast Mg-Y-Nd-Zn-Zr alloy in yield strength. The solid solution strengthening and precipitation strengthening both make the important contribution in strengthening the alloy in as solution treated and aged condition.更多还原