Mg-Gd-Y-Ca-Zr合金的组织和性能研究

发布时间：2018-01-14 23:03

  本文关键词：Mg-Gd-Y-Ca-Zr合金的组织和性能研究　出处：《河南科技大学》2015年硕士论文　论文类型：学位论文

  更多相关文章： Mg-Gd-Y-Ca-Zr合金 显微组织 力学性能 耐蚀性能

【摘要】：稀土镁合金由于其良好的室温及高温力学性能,受到了人们的广泛关注,成为近年来研究的热点。但是稀土金属的价格一般都比较昂贵,致使其不能得到普遍的推广应用。Ca是碱土元素中的一种,其熔点较低,密度与镁的相近,且价格低廉。因此,在稀土镁合金中添加Ca,利用Ca替代或部分替代镁合金中的稀土元素,在保证其力学性能的基础上,降低其经济成本,进而开发含Ca的新型镁合金,会成为一个重要的研究方向。本文以Mg-5Gd-3Y-0.5Zr合金为基础,Ca元素按0.3wt%、0.6wt%、0.9wt%、1.2wt%的比例加入合金中,研究合金的微观组织、力学性能和耐蚀性能。结果表明:Ca含量不同的Mg-Gd-Y-Ca-Zr合金的铸态和固溶时效态显微组织均由α-Mg基体、Mg2Ca、Mg5Gd和Mg24Y5相组成。随着Ca含量的增加,合金的晶粒得到细化,但Ca含量的增加也致使合金的第二相明显增多,在Ca含量为1.2wt%的铸态合金中,第二相在晶界上已呈连续网状分布,且部分覆盖晶界,使晶界轮廓不太清晰。经过固溶时效的热处理工艺后,在同一温度下,随着Ca含量的增加,四种实验合金的抗拉强度都是先升高后降低,在Mg-5Gd-3Y-0.6Ca-0.5Zr合金时抗拉强度最高。在合金成分一定时,四种实验合金的抗拉强度都随温度的升高而下降。合金的延伸率随Ca含量的增加而减小,其断裂方式都属脆性断裂。与Mg-5Gd-3Y-0.5Zr合金相比,加Ca后,无论是室温还是高温,合金的抗拉强度都明显提高,室温下Mg-5Gd-3Y-0.6Ca-0.5Zr合金的抗拉强度达到230MPa,比Mg-5Gd-3Y-0.5Zr合金高出20 MPa以上。Mg-5Gd-3Y-0.6Ca-0.5Zr合金的高温抗蠕变性能良好。在200-300℃温度范围内和50MPa-70MPa应力范围内,其蠕变应力指数n值为1.11-2.92,蠕变激活能Qc的值为147.3-172.7k J/mol,分析其蠕变机制主要是扩散控制机制向晶界滑动和位错滑移控制机制转变。在室温下,对四种实验合金在不同浓度的Na Cl溶液(浓度为0.5%、2.0%、3.5%)中的腐蚀行为进行了研究。合金成分一定时,随着Na Cl腐蚀液浓度的增加,四种实验合金的腐蚀速率均增大。在同一浓度的Na Cl腐蚀液中,合金的耐蚀性能随Ca含量的增加而先增强后减弱,其中Mg-5Gd-3Y-0.6Ca-0.5Zr合金的腐蚀速率最小,耐蚀性能最好。
[Abstract]:Due to its good mechanical properties at room temperature and high temperature, rare earth magnesium alloys have attracted wide attention and become the focus of research in recent years. However, the price of rare earth metals is generally more expensive. As a result, it can not be widely used. Ca is one of alkali soil elements, its melting point is low, its density is close to magnesium, and the price is low. Therefore, Ca is added to rare earth magnesium alloy. Using Ca to substitute or partially replace the rare earth elements in magnesium alloys, on the basis of ensuring its mechanical properties, reducing its economic cost, and then developing new magnesium alloys containing Ca. In this paper, based on Mg-5Gd-3Y-0.5Zr alloy, the content of Ca is 0.3wtand 0.6wt and 0.9wt%. 1.2wt% of the alloy was added to the alloy to study the microstructure of the alloy. Mechanical properties and corrosion resistance. The results show that the as-cast and solid solution aging microstructures of Mg-Gd-Y-Ca-Zr alloys with different content of W Ca are all formed by 伪 -Mg matrix Mg2CA. The phase composition of Mg5Gd and Mg24Y5. With the increase of Ca content, the grain size of the alloy was refined, but the increase of Ca content also resulted in the increase of the second phase of the alloy. In the as-cast alloy with Ca content of 1.2 wt%, the second phase has been distributed continuously on the grain boundary and partially covered the grain boundary, which makes the boundary contour not clear. After the heat treatment process of solution aging, the grain boundary is not clear. At the same temperature, with the increase of Ca content, the tensile strength of the four experimental alloys increased first and then decreased. The tensile strength of Mg-5Gd-3Y-0.6Ca-0.5Zr alloy is the highest. The tensile strength of the four experimental alloys decreased with the increase of temperature, and the elongation of the alloys decreased with the increase of Ca content. Compared with the Mg-5Gd-3Y-0.5Zr alloy, the tensile strength of the alloy increased obviously after adding Ca at room temperature or at high temperature. The tensile strength of Mg-5Gd-3Y-0.6Ca-0.5Zr alloy is 230 MPA at room temperature. 20% higher than Mg-5Gd-3Y-0.5Zr alloy. The creep resistance of Mg-5Gd-3Y-0.6Ca-0.5Zr alloy above MPa is good at high temperature. The stress range is in the range of 200-300 鈩，

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