Bicheng Yang

Thixoforming and Industrial Application of the Semi-Solid Alloy Al-6Si-2Mg

An application of the semi-solid alloy Al-6Si-2Mg to produce automobile components was carried out for farther development of this new alloy. The experiments were done in a self-developed SSM trial line composed of semi-continuous caster combined with electromagnetic stirring for feedstock billet production, 6-station induction reheating equipment for restoring thixotropy of SSM billet and modified die-casting unit for semi-solid thixoforming. The results show that Al-6Si-2Mg alloy has such a suitable fraction solid and low temperature sensitivity of fraction solid that the controllability of SSM process is increased greatly. The billets have uniformly fine microstructure with a higher degree of sphericity and also retain good thixotropic properties. During thixoforming, the die is filled completely, the microstructure of components is dense, and the primary phases are near spherical, and the mechanical property after heat treatment has good performance.

Effects of deformation parameters on microstructure and mechanical properties of magnesium alloy AZ31B

Abstract Plastic deformation and dynamic recrystallization (DRX) behaviors of magnesium alloy AZ31B during thermal compression and extrusion processes were studied. In addition, effects of deformation temperature and rates on the microstructure and mechanical properties were investigated. The results show that the DRX grains nucleate initially at the primary grain boundaries and the twin boundaries, and the twinning plays an important role in the grain refinement. The DRX grain size depends on the deformation temperature and strain rate The average grain size is only 1 μm when the strain rate is 5 s −1 and temperature is 250 °C. It is also found that the DRX grain can grow up quickly at the elevated temperature. The microstructure of extruded rods was consisted of tiny equal-axis DRX grains and some elongated grains. The rods extruded slowly have tiny grains and exhibit good mechanical properties.

Effect of Reheating Process on Microstructure and Mechanical Property of A390 Aluminum Alloy

The effect of reheating process on the microstructure and mechanical property of A390 aluminum alloy and its evolution mechanism was studied. During reheating process, the microstructure of A390 ingots changed greatly, the microstructure of α-Al particles changed from dendrite to spherical. As the reheating temperature increased primary Si and eutectic Si gradually grew up and spheroidized while the mechanical properties got the maximum value as the ingot reheating to 540°C. The relationship the between reheating power and microstructure was built. Improving reheating power can restrain the growth of grains, but if the reheating power was too high, the microstructure becomes non-uniform. It has been found that reheating of A390 aluminum alloy experiences two processes of grain combination and Ostwald growing.

Microstructure and Mechanical Properties of Rheo-Extruded AZ31 Mg-alloy

A new rheo-extrusion technique has been developed to produce extruded profiles. The AZ31 slurry is fabricated by a twin-screw mechanism, and has spheroidal solid particles with a grain size of about 50 to 80μm. The slurry was introduced into an extrusion container with an inner diameter of 95mm, and then squeezed to a billet before extruding into a round bar with a diameter of 22mm using a 500kN extrusion machine. It is found that the new technique has a lower deformation resistance than that of the conventionally hot extrusion technique in the same extrusion velocity. The microstructure and mechanical properties of the rheo-extruded bars were examined in detail. The results illustrated that grains of the bar were very fine with the average grain size about 2.3μm，and the mechanical properties were improved substantially compared with those of the same alloy produced by the conventional hot extrusion.

Hot compressive deformation of rheocast AZ31 magnesium alloy

The billet of magnesium AZ31B was made by twin-screw rheo-cast, and the specimen cut from the rheo-cast billet and normal cast billet were compressed in Gleeble-3000 hot simulator. The deformation temperature was 300, 350, and the strain rates were 0.001~1s-1. The relationship among flow stress, deformation temperature and strain rates were analyzed. The variation of the microstructure was observed and compared after the specimen was hot compressed. The results show that the surface of the rheo-cast specimen is much more smooth than the normal cast specimen after the compression. The dynamic recrystallization had taken place during the compression and the recrystallized grain of rheo-cast sample is more tiny than normal cast specimen.

Effect of Alloying Elements on Mechanical Properties of Al-Si-Cu-Mg Cast Alloys

To develop Al-Si cast alloys with high performance is important for lightweighting vehicles. In this study, the effects of the alloying elements such as Si, Cu, Mg contents (5%-7% Si, 1%-3%Cu, 0.3%-0.9%Mg) on mechanical properties of a test Al-Si-Cu-Mg cast alloy was studied to achieve a specific composition. The experimental results show that the Al-6%Si-3%Cu-0.3%Mg alloy has better comprehensive mechanical properties after T6 heat treatment, which indicates a remarkable interaction of the alloying elements for improving performance.