| Cite this article as: |
Jian Rong, Wenlong Xiao, Xinqing Zhao, Chaoli Ma, Haimiao Liao, Donglei He, Ming Chen, Meng Huang, and Chen Huang, High thermal conductivity and high strength magnesium alloy for high pressure die casting ultrathin-walled components, Int. J. Miner. Metall. Mater., 29(2022), No. 1, pp. 88-96. https://doi.org/10.1007/s12613-021-2318-y
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肖文龙 E-mail: wlxiao@buaa.edu.cn
随着3C产业的快速发展，对具有优异力学性能和高导热镁合金的需求增长迅速。然而，常用压铸镁合金（如Mg–9wt%–1wt%Zn）的导热系数很低。为了使镁合金同时兼具优良的压铸性能和导热性能，本研究选择Al、Zn、RE和Ca作为合金化元素，设计并制备了AZEX4441合金及其手机中框压铸超薄壁件，分析了压铸件的微观结构及力学性能。研究发现，AZEX4441合金具有均匀细小的晶粒，其平均晶粒尺寸为~2.8 μm，第二相主要为沿晶界分布的Al11RE3、Al2REZn2 和Ca6Mg2Zn3相。拉伸测试表明，该合金表现出与AZ91D合金可比的力学性能，其抗拉强度、屈服强度和延伸率分别为233 MPa、185 MPa和4.2%。同时该合金的室温导热系数为94.4 W·m–1·K–1，远高于商用AZ91D合金（53.7 W·m–1·K–1）。通过组织对比分析发现，AZEX4441合金具有较高强度的原因，主要是细小均匀的晶粒所贡献的细晶强化和分布在晶界处的大量金属间化合物产生的第二相强化。相比AZ91D合金，AZEX4441合金凝固过程中各组元之间反应生成了大量的第二相，降低了合金基体中的合金化元素含量，进而使晶格畸变减弱，因此具有较高导热性能的原因。本文为发展高导热压铸镁合金，促进镁合金在3C领域的应用提供了一定的参考价值。
With the rapid development of 3C industries, the demand for high-thermal-conductivity magnesium alloys with high mechanical performance is increasing quickly. However, the thermal conductivities of most common Mg foundry alloys (such as Mg–9wt%–1wt%Zn) are still relatively low. In this study, we developed a high-thermal-conductivity Mg–4Al–4Zn–4RE–1Ca (wt%, AZEX4441) alloy with good mechanical properties for ultrathin-walled cellphone components via high-pressure die casting (HPDC). The HPDC AZEX4441 alloy exhibited a fine homogeneous microstructure (average grain size of 2.8 μm) with granular Al11RE3, fibrous Al2REZn2, and networked Ca6Mg2Zn3 phases distributed at the grain boundaries. The room-temperature thermal conductivity of the HPDC AZEX4441 alloy was 94.4 W·m–1·K–1, which was much higher than 53.7 W·m–1·K–1 of the HPDC AZ91D alloy. Al and Zn in the AZEX4441 alloy were largely consumed by the formation of Al11RE3, Al2REZn2, and Ca2Mg6Zn3 phases because of the addition of RE and Ca. Therefore, the lattice distortion induced by solute atoms of the AZEX4441 alloy (0.171%) was much lower than that of the AZ91D alloy (0.441%), which was responsible for the high thermal conductivity of the AZEX4441 alloy. The AZEX4441 alloy exhibited a high yield strength of ~185 MPa, an ultimate tensile strength of ~233 MPa, and an elongation of ~4.2%. This result indicated that the tensile properties were comparable with those of the AZ91D alloy. Therefore, this study contributed to the development of high-performance Mg alloys with a combination of high thermal conductivity, high strength, and good castability.
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