Jufu Jiang

Preparation and thixoforging of semisolid billet of AZ80 magnesium alloy

Semisolid billet of AZ80 magnesium alloy was prepared by new strain induced melt activated (new SIMA) process and thixoforging experiment was performed. The results show that after as-cast AZ80 magnesium alloy is processed by equal channel angular extrusion, microstructure is refined well due to heavy dynamic recrystallization occurring in severe plastic deformation. Compared with semisolid isothermal treatment and conventional SIMA, semisolid billet with fine and spheroidal grains are achieved in new SIMA. Thixoforging process of semisolid billet prepared by new SIMA has many advantages such as good surface quality of final component, high ability to fill cavity and net-shape. The fine and spheroidal grains and high mechanical properties such as tensile strength of 298 MPa and elongation of 28% can be developed in final part thixoforged.

Microstructure and mechanical properties of AZ61 magnesium alloy prepared by repetitive upsetting-extrusion

Abstract The process of repetitive upsetting-extrusion (RUE) was used to achieve severe plastic deformation (SPD) for an as-cast AZ61 magnesium alloy in temperature range of 285−380 °C. The microstructure and mechanical properties of the as-cast and RUE processed AZ61 alloys were investigated. The results indicated that homogeneous fine-grained structure with mean grain size of 3.5 μm was obtained as the accumulated true strain in the axial direction increased to 4.28 after three RUE passes at 285 °C. The dominant reason of grain refinement was considered the dynamic recrystallization induced by strain localization. It was also found that the microstructural evolution was affected by temperature and accumulated deformation. The mechanical properties of RUE processed AZ61 alloys were significantly improved owing to grain refinement. Furthermore, the relationship between deformation parameters and mechanical properties of AZ61 alloy prepared by RUE processing was revealed by tensile tests carried out at room temperature.

Preparation of semi-solid billet of magnesium alloy and its thixoforming

Abstract Preparation of semi-solid billet of magnesium alloy and thixoforming was investigated by applying equal channel angular extrusion to magnesium alloy. The results show that mechanical properties of AZ91D alloy at room temperature, such as yield strength(YS), ultimate tensile strength(UTS) and elongation, are enhanced greatly by four-pass equal channel angular extrusion(ECAE) at 573 K and microstructure of AZ91D alloy is refined to the average grain size of 20 βm. Through using ECAE as strain induced step in SIMA and completing melt activated step by semi-solid isothermal treatment, semi-solid billet with fine spheroidal grains of 25 βm can be prepared successfully. Compared with common SIMA, thixoformed satellite angle frame components using semi-solid billet prepared by new SIMA have higher mechanical properties at room temperature and high temperature of 373 K.

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.

Effect of process parameters on microstructure and properties of AM50A magnesium alloy parts formed by double control forming

Effects of process parameters on microstructure and mechanical properties of the AM50A magnesium alloy components formed by double control forming (DCF) were investigated via a four-factor and four-level orthogonal experiment. The variable curves of DCF showed that the forging procedure was started in the following 35 ms after the injection procedure was completed. It was confirmed that the high-speed filling and high-pressure densifying were combined together in the DCF process. Better surface quality and higher mechanical properties were achieved in the components formed by DCF as compared to die casting (DC) due to the refined and uniform microstructure with a few defects or without defects. Injection speed affected more effectively the yield strength (YS), ultimate tensile strength (UTS) and elongation as compared to pouring temperature, die temperature and forging force. But the pouring temperature had a more significant effect on hardness as compared to injection speed, die temperature and forging force. Pouring temperature of 675 °C, injection speed of 2.7 m/s and forging force of 4000 kN except for die temperature were the optimal parameters for obtaining the highest YS, UTS, elongation and Vickers hardness. Die temperatures of 205, 195, 195 and 225 °C were involved in achieving the highest YS, UTS, elongation and Vickers hardness, respectively. Obvious microporosity and microcracks were found on the fracture surface of the components formed by DC, deteriorating the mechanical properties. However, the tensile fracture morphology of the components formed by DCF was characterized by ductile fracture due to a large number of dimples and no defects, which was beneficial for improving the mechanical properties.

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.

Microstructure evolution of processed Mg-Al-Zn alloy by equal channel angular extrusion in semi-solid isothermal treatment

Abstract Microstructure evolution of processed Mg-Al-Zn alloy by equal channel angular extrusion(ECAE) in semi-solid isothermal treatment was investigated. The results show that with increasing semi-solid isothermal treatment temperature, the α phase solid grain size of processed Mg-Al-Zn alloy by ECAE increases firstly due to coarsening of α phase solid grains, then decreases due to melting of α phase solid grains. With the increase of extrusion passes during ECAE, the α phase solid grain size in the following semi-solid isothermal treatment decreases. The α phase solid grain size of processed Mg-Al-Zn alloy by ECAE under route B c is the smallest, while the α phase solid grain size of processed material by ECAE under route A is the largest. The primary mechanism of spheroid formation depends on the melting of recrystallizing boundaries and diffusion of solute atoms in the semi-solid state.

Numerical simulation and experiment validation of thixoforming angle frame of AZ61 magnesium alloy

Abstract Numerical simulation and experiment of thixoforming angle frame of AZ61 magnesium alloy were investigated. The results show that with the increase in punch displacement, cylinder billet firstly fills into die cavity of angle frame from feed inlet and plastic deformation occurs in touching region between billet and die cavity. After central thin wall of angle frame is created, semi-solid billet fills toward two edges. Lastly, complete plastic deformation occurs in billet, leading to complete filling of semis-olid billet. Effective strain, effective stress and billet temperature decrease with the increase in punch displacement. Effective stress decreases with the increase in billet temperature, die temperature and punch velocity. The optimal conditions decided by numerical simulation are as follows: die temperature of 450 ?, billet temperature of 560 ? and punch velocity of 30 mm/s. Angle frame components with high mechanical properties such as yield strength of 225 MPa, tensile strength of 309 MPa and elongation of 21.8% and fine microstructure could be thixoformed successfully according to process parameters decided by numerical simulation.

Preparation of AZ91D magnesium alloy semi-solid billet by new strain induced melt activated method

New strain induced melt activated (new SIMA) method for preparing AZ91D magnesium alloy semi-solid billet is introduced by applying equal channel angular extrusion into strain induced step in SIMA method, by which semi-solid billet with fine spheroidal grains and average grain size of 18 μm can be prepared. Furthermore, average grain size of semi-solid billet is reduced with increasing extrusion pass of AZ91D magnesium alloy obtained in ECAE process. By using semi-solid billet prepared by new SIMA, thixoforged magazine plates component with high mechanical properties such as yield strength of 201.4 MPa, ultimate tensile strength of 321.8 MPa and elongation of 15.3%, can be obtained.

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.