Continuous Casting And Extrusion(CASTEX) Process Of Zn-based Alloys And Their Microstructure And Mechanical Properties

Zn and Zn-based alloys have been widely used in thermal spraying, surface modification of capacitors, hardware accessories, electronics, industrial equipments and automotive industries because of their good performance, such as good corrosion resistance and wear-resistance, high mechanical properties and so on. At present the Zn and Zn-based alloy rods or wires are presently cast or extruded. It is noted that the strength and ductility of deformed Zn alloys are much higher than the corresponding cast ones. The continuous casting and extrusion technique (CASTEX) is a kind of integration forming process with the characteristics of short-course and cost-effective processing, which has been widely used to prepare Al alloys wires with improved mechanical properties. However, So far there have been few reports on CASTEX processing to prepare Zn alloys. Therefore, in this paper, the Zn-Al-based and Zn-Cu-based alloys have been fabricated by the CASTEX forming and their micro structures and mechanical properties are also investigated in detail.The Zn-(2～27) wt.%Al-based and Zn-(2-4) wt.%Cu-based Zn alloys are firstly prepared by the CASTEX forming processing in this study, and the surface quality of the products can be well controlled. The tensile strength of the CASTEX formed ZA27alloy increases from220MPa to420MPa, when it is treated at350℃and subsequently aged at150℃for30min. However, its ductility has no obvious change as compared to that of CASTEX state. It suggests that the mechanical properties of Zn-based CASTEX alloys can be improved by the subsequent heat treatments. The ductility of the Znl5Al CASTEX alloy is improved with decreasing the pouring temperatures, i.e., when the pouring temperatures are600,560and530℃, the corresponding elongations are0.75,34and64%, respectively. And the tensile strength of Zn15Al alloy is slightly changed namely, that is196,235and210MPa corresponding to the pouring temperatures,600,560and530℃,respectively. It indicates that the mechanical properties of the Zn-based CASTEX alloys can be improved by controlling temperature distribution field in the CASTEX processing, especially for their ductilities. On the other hand, when the pouring temperature remains600℃, the ductility of Zn15Al CASTEX alloy increases due to a small amount addition of Bi or Ce. When the0.2wt.%Bi is added, the elongation increases to5.3%while the strength decreases from196MPa to179MPa. When the0.2wt.%Ce is added, both the elongation and tensile strength increase to17.8%and230MPa, respectively. It means that the mechanical properties of the Zn-based alloys can be improved by micro-alloying method, in particular for the ductility when the CASTEX process remains no change,. For two types of Zn-based alloys with lower Al content, the tensile strength and elongation of the CASTEX Zn4Al zinc alloy are197MPa and20%, respectively, when the pouring temperature is450℃. The tensile strength and elongation of the CASTEX Zn2Al Zn alloy is199MPa and1.2%, respectively, when the pouring temperature is500℃. For two kinds of CASTEX Zn-Cu based alloys, when the pouring temperature is600℃, the tensile strength and elongation of the Zn3.5Cu zinc alloy is300MPa andl.4%, respectively. When the pouring temperature is610, the tensile strength and elongation of the Zn2.5Cu zinc alloy is285MPa andl.2%, respectively.The mechanical properties of the present CASTEX Zn alloys are relatively lower than that of commercially deformed Zn alloys. However, it is be believed that the mechanical properties of the CASTEX Zn alloy should be further improved to be equal-valued to or better than the corresponding deformed Zn alloys, by optimizing the processing and modifying equipment forming ability of the CASTEX.