【作者】 张玉华；

【导师】 张金山；

【作者基本信息】 太原理工大学 ， 材料加工工程， 2010， 硕士

【摘要】 Mg-Zn-Al系合金由于具有高温性能较好、成本较低和铸造性能较好等方面的优势,被认为是一种有发展前途的高温镁合金。高锌镁合金的Zn含量一般在5wt.%以上,主要热强相为τ-Mg32（Al,Zn）49相和少量的φ-Al2Mg₅Zn₂相,但其铸造性能还未达到令人满意的程度,容易产生热裂倾向,并且常温和高温力学性能不能同时兼顾等方面也还存在问题。为了改善Mg-Zn-Al系合金所存在的力学性能方面的问题,本文选择以Mg-10Zn-5Al（ZA105）高锌镁合金为基础,以Sb为变质剂,Cu为合金化元素,优化合金成分,开发了一种新型低成本高锌镁合金。试验中采用金相组织观察（OM）、X射线衍射仪（XRD）、扫描电子显微镜（SEM）、能量散射光谱（EDS）、显微硬度、冲击韧度以及常温和高温拉伸性能测试等分析手段,系统地研究了添加不同含量Sb、Cu合金元素及不同热处理工艺对Mg-10Zn-5Al镁合金显微组织及力学性能的影响,以期为高锌镁合金综合力学性能的提高提供依据。Sb的变质作用研究结果表明:Mg-10Zn-5Al-2Cu合金的显微组织由α-Mg基体、τ-Mg32（Al, Zn）49相、φ-Al2Mg₅Zn₂相和Mg₂Cu组成。与无变质的Mg-10Zn-5Al-2Cu合金相比,加入Sb后的合金中出现新的高熔点,具有六方D52结构的黑色Mg₃Sb₂弥散颗粒组织。Sb含量为0.1wt.%时,合金组织细化效果最明显。随着Sb量的增加,Mg-10Zn-5Al-2Cu镁合金的布氏硬度呈现出逐渐上升的趋势。当Sb量增加至0.1wt.%时,冲击韧度上升达到最大值6 J/cm2,比不含Sb时Mg-10Zn-5Al-2Cu镁合金的冲击韧度提高了50%,而合金的抗拉强度也达到190MPa。特别是Sb的含量为0.2wt.%时,合金的抗拉强度达到最大值195 MPa,较之不加Sb时提高5.4%,但其冲击韧度急剧下降。Sb量大于0.2wt.%时,合金的拉伸强度也开始逐渐下降。为此,本实验条件下,Sb合适的加入量为0.1wt.%,Mg-10Zn-5Al-2Cu镁合金的组织细化效果最好,具有良好的综合力学性能。Cu的合金化分析结果显示:Mg-10Zn-5Al-0.1Sb高锌镁合金中Cu的加入使合金第二相τ-Mg32（Al, Zn）4相上出现了新的鱼骨状Mg₂Cu相。合金中Cu的加入量不超过2.0wt.%时,随着Cu量的增加,合金的硬度、拉伸强度逐渐上升,冲击韧度逐渐下降。特别在Cu的含量为2.0wt.%时,合金的硬度达到最大值79.35HB,较之不加Cu时提高了9.65%;室温和高温（200℃）拉伸强度也达到190MPa和160MPa,比不加Cu时分别提高了21.1%和14.3%,但冲击韧度开始升高达6 J/cm2。随着Cu量的继续增加,合金的显微组织粗大化,其硬度、拉伸强度和冲击韧度均开始降低。因此,在本实验条件下,Cu的合适加入量为2.0wt.%,Mg-10Zn-5Al-0.1Sb高锌镁合金的合金化效果最明显,具有较高的力学性能。热处理的试验结果表明:（1）经过固溶处理后的Mg-10Zn-5Al-0.1Sb-XCu合金,晶界上τ-Mg32（Al,Zn）49相和晶内φ-Al2Mg₅Zn₂相周围的共晶α-Mg相均溶入到基体组织中,组织中第二相τ-Mg32（Al,Zn）49相的形状及分布都发生了明显的变化。但固溶处理并没有使晶界上的第二相τ相完全固溶到基体中,在晶界处仍存在高熔点的热稳定相τ-Mg32（Al,Zn）49相和Mg₂Cu相。与铸态合金相比,经过固溶处理24h后的Mg-10Zn-5Al-0.1Sb-XCu试验合金,基体的显微硬度明显提高,提高到85 Hv,比铸态合金提高了16.6%。（2）经过时效处理36h后的Mg-10Zn-5Al-0.1Sb-XCu合金,弥散分布的三元沉淀相会在晶界以及附近最大量析出,析出的三元沉淀强化相主要是τ-Mg32（Al,Zn）49相和φ-Al2Mg₅Zn₂相。合金的时效时间进一步延长至48h时,合金析出的三元相发生聚集长大。合金的显微硬度随时效时间的延长呈现先增长后降低的趋势。时效时间为36h时,合金的显微硬度达到最大值105.9Hv,比固溶时合金的显微硬度（85 Hv）提高了24.6%;随时效时间继续延长,合金显微硬度下降。固溶+时效处理后的实验合金,其室温和高温拉伸强度均比铸态要提高很多,但其变化趋势与铸态时一致。当Cu的含量为2.0wt.%时,固溶+时效处理后合金的室温和高温（200℃）拉伸强度分别达到228 MPa和176MPa,比铸态时提高了20%和10%。因此,本实验条件下,合金的最佳时效时间为36h。更多还原

【Abstract】 Mg-Zn-Al alloy has been considered as a promising high-temperature magnesium alloy because of its high heat-resistance, lower cost and sound castiability. Generally, the main heat-resistant phases areτ-Mg32（Al,Zn）49 phase and a small amount ofφ-Al2Mg₅Zn₂ phase in ZA alloy, in which Zn content is above 5wt.%. However, the casting properties of this alloy are unsatisfactory and there are still some problems in mechanical properties both at elevated temperature and at room temperature. Therefore, in order to solve these problems, the new typical and low-cost high zinc magnesium alloy was developed by optimizing alloy composition of Mg-10Zn-5Al alloy in which Sb was used as modifier and Cu as alloying element.Effect of Sb、Cu and heat treatment on microstructure and mechanical properties of Mg-10Zn-5Al magnesium alloy were investigated by using modern analytical technology of optical microscopy（OM）, X-ray diffraction（XRD）, scanning electron microscopy（SEM）, energy dispersive spectroscopy（EDS）, micro-hardness test, impact-toughness test and tensile-strength test, hoping to provide theoretical foundation for the improvement of mechanical properties of high-zinc magnesium alloy.Results of Sb-added alloys indicate that : the microstructure of the Mg-10Zn-5Al-2Cu alloy are composed ofα-Mg、τ-Mg32（Al,Zn）49 phase、φ-Al2Mg₅Zn₂ phase and Mg₂Cu phase. Compared with the unmodified Mg-10Zn-5Al-2Cu alloy, the new dystectic Mg₃Sb₂ black particles with hexagonal D52 structure appear in the matrix. When the content of Sb is 0.1wt.%, the microstructures of the alloy is refined dramatically. The hardness of Mg-10Zn-5Al-2Cu alloy shows a gradually rising tendency with Sb increasing. When the addition amount of Sb is 0.1wt.%, the impact-toughness rises to the maximum 6J/cm2, which is 50% higher than that of Sb-free alloy, and the tensile strength is up to 190MPa. In particular, when the content of Sb is 0.2wt.%, the tensile-strength reaches the maximum 195 MPa, which increases by 5.4%, while the impact-toughness drops sharply. As the addition of Sb exceeds 0.2wt.%, the tensile-strength begins to decline either. So the appropriate Sb addition is 0.1wt.% in the experiment. The microstructure of Mg-10Zn-5Al-2Cu magnesium alloy is the most refined and better comprehensive mechanical properties are achieved.The analysis results of Cu strengthening indicate that: Cu addition into the Mg-10Zn-5Al-0.1Sb high-zinc magnesium alloys results in formation of the fishbone-like Mg₂Cu eutectic structure on theτ-Mg32（Al, Zn）49 second phase in the alloy. When the Cu addition is less than 2.0wt.%, the hardness and the tensile-strength arise gradually with the Cu increasing, while the impact-toughness shows downward trend. Especially when the content of Cu is 2.0wt.%, the hardness reaches the maximum, 79.35HB, 9.65% higher than that of mother alloy. The room temperature and elevated temperature （200℃） tensile strengths reach 190MPa and 160MPa, which increase by 21.1 % and 14.3%, while the impact-toughness is up to 6 J/cm2. Further Cu addition leads to the coarseness of microstructures and rapid decrease of hardness, tensile-strength, and impact-toughness. In a word, the microstructure of Mg-10Zn-5Al-0.1Sb magnesium alloy is the most strengthened and better comprehensive properties are obtained with appropriate Cu addition of 2.0wt.%.The experiment results of heat treatment indicate that:（1） After solution treatment, the eutecticα-Mg phase around in vicinity of grain boundaries and theφ-Al2Mg₅Zn₂ phase in grains of the Mg-10Zn-5Al-0.1Sb-2.0Cu alloy dissolve into to the matrix microstructure. And micro-morphology and distribution of theτ-Mg32（Al,Zn）49 phase change obviously. But theτ-Mg32（Al,Zn）49 phase does not completely dissolve into the matrix in the solid solution treatment. Dystectic heat-stabilityτ-Mg32（Al,Zn）49 phase and Mg₂Cu phase still exist at the grain boundaries, the micro-hardness of the matrix in the Mg-10Zn-5Al-0.1Sb-2.0Cu alloy is up to 85 Hv, which is 16.6% higher compared with as-cast alloys after 24h solution treatment.（2） The massive ternary phases are precipitated at or around grain boundary in Mg-10Zn-5Al-0.1Sb-2.0Cu alloy aging for 36h. The precipitated ternary strengthening phases are identified asτ-Mg32（Al,Zn）49 phase andφ-Al2Mg₅Zn₂ phase. With aging time elongating to 48h, the ternary precipitations enrich and grow. The micro-hardness increase first and then decrease with the elongating of aging time. When the aging time is 36h, the micro-hardness is up to the maximum, 105.9Hv, 24.6% higher than that of alloys in solid solution state. Tensile strengths at room temperature and high temperature by solution and ageing treatment are much higher than that of as-cast alloys and variation tendency of tensile strengths is the same as that of as-cast alloys. When the addition of Cu is 2.0wt.%, the tensile-strengths of solution and ageing treated alloys at room temperature and high temperature （200℃） are 228MPa and 176MPa, which are 20% and 10% higher than that of as-cast alloys respectively. Therefore, the optimal aging time in the experiment is 36h.更多还原