Shoujing Luo

Microstructural evolution of AZ61 magnesium alloy predeformed by ECAE during semisolid isothermal treatment

Abstract The microstructural evolution of AZ61 magnesium alloy predeformed by equal channel angular extrusion (ECAE) during semisolid isothermal treatment (SSIT) was investigated by means of optical metalloscopy and image analysis equipment. The process involved application of ECAE to as-cast alloy at 310 °C to induce strain prior to heating in the semisolid region for different time lengths. The results show that extrusion pass, isothermal temperature and processing route have an influence on microstructural evolution of predeformed AZ61 magnesium alloy during SSIT. With the increase of extrusion pass, the solid particle size is reduced gradually. When isothermal temperature increases from 530 °C to 560 °C, the average particle size increases from 22 μm to 35 μm. When isothermal temperature is 575 °C, the average particle size decreases. The particle size of microstructure of AZ61 magnesium alloy predeformed by ECAE at B C during SSIT is the finest.

Microstructure and mechanical properties of AZ61 magnesium alloy parts achieved by thixo-extruding semisolid billets prepared by new SIMA

Abstract New strain induced melt activation (new SIMA) method was employed to prepare high-quality semisolid billet of AZ61 magnesium alloy. Optical microscopy and tensile test were used to study the microstructure and mechanical properties of the thixo-extruded component. The results showed that the optimal process parameters for achieving the complete filling status involved the applied pressure of 784 MPa, the pressure holding time of 90 s and the die temperature of 450 °C. Compared to semisolid isothermal treatment, high mechanical properties such as the tensile strength of 300.5 MPa and elongation of 22% and fine microstructure were obtained in the thixo-extruded parts. With increasing the isothermal temperature and holding time, the tensile strength and elongation were increased firstly and then decreased. When the press pass was increased from 1 to 4, the tensile strength and elongation of the thixo-extruded parts were greatly enhanced and microstructure was refined obviously.

Research into the properties and microstructure of ZA13 alloy tubes formed by liquid extrusion

Abstract Liquid extrusion is a new type of forming process developed on the basis of the characteristics of both squeeze casting and solid extrusion. With this process, many types of tubes, bars, and shaped products can be produced. Compared with traditional processes, the production steps can be simplified, and the end item can be obtained directly in a single process. In this paper, the characteristics of the process are introduced, the emphasis being put on research into the influence of liquid extrusion on the microstructure and properties of ZA13 alloy, including the mechanical properties, the wear resistance, the micromorphology and the fractography. It can be seen clearly, that all of the properties have been enhanced substantially, the microstructure has been altered, and the attributes of the material have been changed after the process. Furthermore, the strenghening mechanism of liquid extrusion has been expounded and the viewpoint of the twice-strengthening to materials by the process has been advanced by the authors. All of these have proven that there appears to be a great future for the liquid extrusion process.

Microstructure and properties of AZ80 alloy semisolid billets fabricated by new strain induced melt activated method

Abstract AZ80 alloy semisolid billets were fabricated by a new strain induced melt activated method (SIMA), which involved the predeformation of as-cast AZ81 alloy via equal channel angular extrusion (ECAE) and the following semisolid isothermal treatment of ECAE-processed AZ80 alloys. The results show that highly strain-induced effect is successfully achieved by ECAE due to refined microstructure and the mechanical properties are enhanced. High-quality AZ80 semisolid billets with fine and spherical grains are fabricated by new SIMA method. The results of thixoforged experiment confirm that enhanced mechanical properties including yield strength of 216.9 MPa, ultimate tensile strength of 312.4 MPa and elongation of 26% are successfully achieved. It also confirms that new SIMA method is a very desirable method for fabricating AZ80 alloy semisolid billets.

The effect of plastic flow on the strengthening and toughening of alloy during liquid-metal forming under pressure

Abstract Liquid-metal forging and liquid extrusion are two typical technologies in the forming of liquid metal under pressure. The mechanical properties of the material processed by the two technologies can be enhanced greatly compared with those for traditional casting technology. In particular, the plasticity and the toughness increase by 10–20 times. The technologies open up a new way for the forming of brittle and difficult-to-deform alloys. However, there is a great difference between the degrees of improvement of the mechanical properties arising from the employment of the two different technologies, the improvement for liquid-metal forging being much less than that for liquid extrusion. The processes of the two technologies are studied in this paper. It is found that flowing solidification (occuring in the liquid-solid zone) and plastic flow (occuring in the solid zone) are the essential reasons which cause the above difference. The corresponding experiments show that the rate of nucleation is increased by flowing solidification and that casting defects are eliminated completely by plastic flow. For liquid-metal forging, the mechanism of strengthening and toughing of alloys is mainly dynamic solidification under pressure, the influence of plastic deformation being slight. For liquid extrusion, in addition to flowing solidification under pressure, plastic flow plays a very important role.