| In order to improve the strengthening and toughening as well as high temperature properties of high zinc Mg-Zn-Al alloy system, the optimal Zn content of base Mg-Zn-Al alloy was determined by position, melting, heat treatment as well as alloying element adding method optimization based on the previous research results and drawbacks. After that, Sb and Cu were added into base alloy and the effect of Sb and Cu addition on the microstructure, mechanical properties and wear as well as corrosion characterization was studied. In addition, the effect of master alloy in the form of Al-Ce contained Sb, Ti and Mn on the microstructure and mechanical properties of base alloy was also investigated. Furthermore, the influence of heat treatment on the microstructure and mechanical properties of ZA105alloy containing different Cu was researched.Firstly, the effect of Zn content on the microstructure and mechanical properties of Mg-Zn-Al alloy was studied. The results indicated that (1) The microstructure of as-cast Mg-10Zn-5Al alloy is composed of α-Mg, τ-Mg32(Al, Zn)49and φ-Al2Mg5Zn2phases. As the Zn content is10wt.%, namely Zn/Al ration equals to2, most of the τ phase and a few cp phase distributed in the matrix in the form of semi-continuous lath and/or massive;(2) The hardness increased and the tensile strength increased firstly and then decreased while the impact toughness decreased with increasing Zn content. Mg-10Zn-5Al (ZA105) alloy presents the best combination of strength and toughness. Therefore, ZA105alloy was determined as base alloy.Secondly, the effect of Sb addition on the microstructure, mechanical properties and wear as well as corrosion characterization was investigated. The results indicated that (1) The microstructure of as-cast Sb containing Mg-10Zn-5Al-0.1Sb alloy is composed of a-Mg, x-Mg32(Al, Zn)49, MgZnCu (p-Al2Mg5Zn2and Mg3Sb2phases, whereα-Mg3Sb2is thermal stable phase with high melting point and D52structure;(2) As the Sb addition is0.1wt.%, the microstructure was refined greatly and the T-Mg32(Al, Zn)49phase changed from semi-continuous lath to massive; meanwhile, black granular Mg3Sb2phase was formed on τ and φ phases;(3) The hardness increased and the tensile strength as well as impact toughness increased firstly and then decreased with increasing Sb content. The impact toughness of the alloy with0.1wt.%addition of Sb improved by50%as that of the one without Sb addition, while the tensile strength increased by5.4%as the Sb addition reached to0.2%;(4) The wear capacity of the alloy increased firstly and then decreased as Sb content increased, resulting in the minimal wear loss as the Sb content being0.8wt.%;(5) the corrosion rate in3.5wt.%NaCl increased slightly with increasing Sb content. The addition of Sb has little effect on the corrosion products, which were mainly composed of Mg(OH)2, MgO and MgCl2;(6) Polarization curve of Sb-containing alloy shifted to the direction of negative potential, and free corrosion potential decreased, the addition of Sb could restrict cathodic reaction during corrosion and have little effect on anodic reaction.(7)After addition of Sb, the damping mechanism of the studied alloys can be explained in terms of pinning and de-pinning mold. The above mentioned results are associated with the interaction of dislocation damping, interface damping and grain boundary damping.Thirdly, the effects of Cu addition on the as-cast microstructure, mechanical properties, wear behavior and corrosion characterization of high Zn Mg-10Zn-5Al-0.1Sb alloy was investigated. The results indicated that:(1) The microstructure of the alloy is composed of α-Mg, τ-Mg32(Al,Zn)49,(p-Al2Mg5Zn2and MgZnCu phases. Note that the MgZnCu phase is thermal-stable phase with melting point of565℃;(2) As the addition of Cu is2.0wt.%, the microstructure refinement is best, with more addition of Cu, the microstructure coarsen can be observed and black herringbone-like phase MgZnCu increased;(3) among the Cu-containing alloys, the alloy with the addition of2.0wt.%Cu exhibits the relatively optimum mechanical properties. The hardness, room and elevated-temperature strengths of2.0wt.%Cu-containing alloy are79.35HB,190MPa and160MPa, respectively, which increased by9.65%,21.1%and14.3%compared to those of Cu-free one;(4) The wear capacity decreased and then increased with increasing Cu content, namely wear resistant ability increased firstly and then decreased. Among the Cu-containing alloys, the alloy with the addition of2.0wt.%Cu exhibits the best wear-resistant behaviors;(5) Corrosion rate of the alloy increased firstly and then decreased as Cu content increased during immersion tests in3.5wt.%NaCl solution, mass loss increased as increasing corrosion time. Among the Cu-containing alloys, the alloy with the addition of2.0wt.%Cu exhibits the lowest corrosion rate. The corrosion products are mainly composed of Mg(OH)2, MgO and MgCl2;(6) The cathodic parts of the and anodic parts of the curve were not asymmetric and the addition of Cu is favorable to promote the cathodic reaction during corrosion processing.(7)The effect of Cu on the Macro-damping behavior is under the control of dislocation damping, interface damping and grain boundary damping. ZA105containing1.Owt.%exhibited the best damping properties.Furthermore, the effect of addition of Al-Ce based master alloy on the microstructure and mechanical properties was investigated. The results indicated that (1) after addition of master alloy, the alloy was composed of a-Mg, τ-Mg32(Al,Zn)49, φ-Al2Mg5Zn2and Al4Ce phases. As the addition content of Al-40Ce-5Ti-5Sb alloy was2.0wt.%or Al-20Ce-5Ti-5Sb-5Mn master alloy was3.Owt.%,τ and φ phases in the alloys changed into small massive and the Al4Ce phase was formed;(2)The hardness of the alloy increased as the increasing content of the added master alloys, The maximal room and elevated-temperature strengths of2.0wt.%Al-40Ce-5Ti-5Sb-containing alloy are195and152MPa, respectively, which increased by8.33%,16.92%compared to those of Al-40Ce-5Ti-5Sb-free one. Similarly, the maximal room and elevated temperature strengths and impact toughness of3.0wt.%Al-20Ce-5Ti-5Sb-5Mn containing alloy are198,155MPa and9.21J/cm2, respectively, which increased by10.00%,19.23%and26.69%compared to those of Al-20Ce-5Ti-5Sb-5Mn free one.Finally, the influence of heat treatment on the microstructure and mechanical properties of ZA105alloy with different content of Cu was investigated. The results indicated that (1) the microstructure of the alloy after solid solution treatment at350℃for24h and aged at180℃was mainly composed of a-Mg,τ-Mg32(Al,Zn)49, φ-Al2Mg5Zn2and MgZnCu phases. After solid solution, the strip-like τ and φ phases changed into fine granular phases. Some thermal stable phases such as τ phase and MgZnCu phases remained at the grain boundary after solid solution treatment. Hv hardness of the matrix after solid solution increased by16.7%compared to that of as-cast one, being85.1HV, however, the Hv hardness of τ phase decreased a little;(2) Fine granular τ-Mg32(Al,Zn)49phase precipitated at and around the grain boundaries after aging treatment, and peak aged condition occurred at70h with the peak hardness being108.2Hv,27.1%higher than that of solid solution one, as the aging time over100h, aggregation and growth of τ phase occurred and the hardness declined. There is no obvious change of MgZnCu phase due to its thermal stability;(3) The room/elevated temperatures tensile strength of as-cast and heat treated alloys increased with increasing Cu content, after T6treatment, the room/elevated temperatures tensile strengths of the Cu2.0wt.%-containing alloys further increased by18%and10%compared to those of as-cast alloys due to the second phase strengthening, being225MPa and176MPa, respectively.
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