Shou-jing Luo

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.

Theory and application research development of semi-solid forming in China

Abstract In order to adapt to the trend of “energy saving and emission reduction” and impel the practical application of semi solid processing (SSP) in China, the progress and application of semi-solid theory in China have been reviewed briefly and systematically. It was emphasized on basic theories, such as formation of globular grains, rheology, high pressure solidification and plastic deformation and applications, such as material design, preparation of semi-solid billets (slurries), thixoforming and application status, which are based on the advantage of semi-solid processing. The results show that the gap of SSP between world level and China exists, especially in application technologies, including market recognition, application fields exploiting, developing of billets (slurries) preparation technologies with low cost and special equipments. The prospect of semi-solid forming development path in China is presented. And we hope that application of SSP has great new breakthrough and development and China will be changed from a large metal processing country to a powerful metal processing country.

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.

Steady state Theological behavior of semi-solid ZK60-RE magnesium alloy during compression

Steady state rheological behavior of semi-solid ZK60-RE magnesium alloy during compression was studied. The alloy was prepared from ZK60 alloy and RE elements by casting, equal channel angular extruding, and liquidus forging. Semi-solid isothermal pre-treatment was carried out to make the grains spherical before compression. The apparent viscosity increases with decreasing the solid content and shear rate. Another very important factor is the grain size. When the solid content is high, the viscosity increases with decreasing the grain size at high strain rates and decreases with decreasing the grain size at low shear rates. Several fitting equations were obtained by using the power law equation, and the method of time-temperature superposition was used to get more information through a small number of experimental data.

Pseudo-semi-solid thixoforging of cup shell with Al/Al2O3

Abstract A new technology — the thixoforging of ceramics/metal composites in pseudo-semi-solid state was proposed based on the powder metallurgy technology combined with semi-solid metal forming process, and the cup shell of automobile piston with Al 2 O 3 /Al composites was prepared. It is proved through metallographic analyses and three-point bending tests that the technology is feasible for the ceramics/metal composites forming. The results show that the tough strength and the degree of hardness of the samples with certain plasticity are high. It will play a very large role in accelerating the ceramics composites and high melt point materials use in more fields and tamp the foundation for further studies of this technology.

Effect of heat treatment on mechanical properties of thixoformed 7A09 aluminum alloy

Abstract The effects of solution-ageing treatment on the mechanical properties of semi-solid metal (SSM) products were studied by the method of orthogonal experiment. The microstructure and tensile properties at different treatment conditions were analyzed. The results show that the effects of solution-ageing treatment were obviously influenced by the original microstructure of the SSM billet. Higher temperature is favorable for the sufficient solution of alloy elements, but the grains will grow up when treated at a higher temperature or soaked for a longer time. There is a contradiction between the maximum tensile strength and elongation percentage. Under the condition of solution treatment at 475 °C for 12 h and at 133 °C for 20–22 h ageing, better properties including about 540 MPa of tensile strength and more than 6.3% of elongation can be obtained in general. The surplus phases not melted in the substrate and the solution precipitated supersaturated elements are the main factors influencing the properties of the alloys.

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.

Uniformity and continuity of effective strain in AZ91D processed by multi-pass equal channel angular extrusion

Abstract AZ91D magnesium alloy was processed by equal channel angular extrusion(ECAE). The influence of extrusion temperature, extrusion pass and extrusion route on the ultimate strength of the extruded billet was analyzed. The process of multi-pass extrusion was simulated with the method of finite element analysis, and the continuity and uniformity of effective strain in multi-pass extrusion were investigated. The results show that extrusion pass plays the most important role in improving the ultimate strength of AZ91D magnesium alloy, the extrusion route is the second, and the extrusion temperature is the last. From the numerical simulation, there exists the continuity of the accumulated deformation in multi-pass extrusion and the effective strain increases linearly. The tendency of the strain uniformity is different in multi-pass extrusion with extrusion routes. The results of experiment agree with those of numerical simulation.

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.