Xiangjie Wang

Effect of combined application of electromagnetic fields on horizontal direct chill casting of 7050 aluminium alloy

Abstract Influence of combined electromagnetic field application on horizontal direct chill casting of 7050 aluminium alloy is investigated. Temperature measurement and structure observation are carried out to analyse the casting process under different electromagnetic fields. Combined electromagnetic field can reduce the harmful gravitational thermal effect in the horizontal direct chill casting process and improve the ingot properties. With application of combined electromagnetic field, temperature distribution in the melt is more uniform, sump of the ingot becomes flat and symmetric, surface quality of ingot improves markedly, grain morphology changes from feathery grains to equiaxed grains and grain size decreases. Distribution of copper and zinc in the transverse section of the ingot becomes more uniform.

Effect of electromagnetic field on microstructure and macrosegregation of flat ingot of 2524 aluminium alloy

Low frequency electromagnetic casting (LFEC) process with the application of an induction coil outside the conventional direct chill (DC) casting mould was used to prepare the flat ingot of 2524 alloy and the effect of electromagnetic field on the microstructure and macrosegregation of this alloy was systematically studied. The results show that the flat ingot prepared by the LFEC process has a finer and more uniform as-cast microstructure and the grain morphology is transformed from dendrite and rosette-like to equiaxed structure. The LFEC process also shows a significant effect on macrosegregation, and with the application of electromagnetic field during casting process, the segregation in the centre of the ingot is obviously reduced. The mechanism of these effects was also discussed.

Effect of low frequency electromagnetic field on as casting structure and surface quality of horizontal direct chill casting 7075 alloy

Abstract Horizontal direct chill (HDC) casting is a well established production route for aluminium alloy ingots; however, the ingots may suffer from inhomogeneous microstructures and serious macrosegregation due to the unbalanced cooling condition and gravitational effect. The present study considers the HDC casting of 7075 aluminium alloy ingot under the influence of a low frequency electromagnetic field (LFEF). Temperature measurement is employed to analyse the effect of LFEF on the HDC casting process. Surface topography and structure observation are conducted to analyse the effect of LFEF on the surface and interior quality of the HDC ingot. The results show that the LFEF can effectively uniformalise the thermal distribution, flatten the sump shape, improve the ingot surface quality, promote a transition from columnar/feathery to equiaxed dendritic growth and has a distinct grain refining effect.

Effects of dynamic recrystallisation during deep rolling of semisolid slab and heat treatment on microstructure and properties of AZ31 alloy

Abstract A novel process of manufacturing high performance AZ31 alloy strip was put forward by combining semisolid rolling, deep rolling and heat treatment, and the effects of dynamic recrystallisation during deep rolling of semisolid slab and heat treatment on microstructure and properties of AZ31 alloy were investigated. When the casting temperature was set from 650 to 690°C and the vibration frequency was controlled at 80 Hz, AZ31 alloy strip with the cross-section size of 4×160 mm and fine near round and rosette grains was manufactured by semisolid rolling. Dynamic recrystallisation happened during deep rolling process. Dynamic recrystallisation grain size decreases with the increase in deep rolling temperature in a certain scope. With the increase in deep rolling deformation amount, the microstructure evolved gradually from coarse primary grains and twins to fine dynamic recrystallisation grains and twist primary grains as well as small regular equiaxed grains. AZ31 alloy strip with very fine equiaxed grain in size of 6 μm was obtained by deep rolling. After solution treatment at 415°C for 20 h, the saturated solid solution of AZ31 alloy strip has been formed. After solution treatment at 415°C for 20 h and aging at 230°C for 16 h, the deep rolled AZ31 alloy strips exhibit excellent mechanical properties; the ultimate tensile strength, yield strength, elongation to failure and hardness could reach 330 MPa, 204 MPa, 11% and 71 HV respectively.

Effects of low frequency electromagnetic field on solidification of 7050 aluminium alloy during hot top casting

Abstract On the basis of conventional hot top casting, low frequency electromagnetic field is applied during conventional hot top casting process. Effects of low frequency electromagnetic field on cold fold, macrostructure, microstructure and sump shape have been studied. The experimental results show that with the application of the low frequency electromagnetic filed, the as cast structure has been refined, the depth of cold fold is decreased, the upstream conduction distance becomes long, and the sump becomes shallow. The reasons for the low frequency electromagnetic field refining the structure of the ingot, making the upstream conduction distance long and the sump shallow were summarised.

Microstructure evolution during novel rheorolling process for producing A356 alloy strip

Abstract Microstructure evolution during a novel rheorolling process for producing A356 alloy strip was investigated. Under the high cooling rate caused by the sloping plate and stirring action caused by the vibration and metal flow, high nucleation rate and dendrite breakage happened during the process, which causes the formation of fine spherical or rosette primary grains. The grain size of the primary α-Al phase decreased with the decrease in casting temperature in the cooling slope, but the volume fraction of the primary α-Al phase increased. The change of the primary grain shape is not obvious in the roll gap during the rolling process, and most of the primary grains nearly kept round or rosette shapes. When the casting temperature is 660°C, the strip with a cross-section of 4×160 mm was produced, and homogeneous microstructure was obtained.

Dynamic strain aging precipitation of Mg17Al12 in AZ80 magnesium alloy during multi-directional forging process

Dynamic aging precipitation of Mg17Al12 phases in AZ80 magnesium alloy was studied by multi-directional forging (MDF) with decreasing temperatures from 410 to 300 °C. The results show that the morphology of the dynamically precipitated β-Mg17Al12 phases (formed during forging process) exhibited granular shape. During the multi-directional forging process, the inhomogeneous dynamic precipitation of the β-Mg17Al12 phases result in the coexistence of the fine grains (with many granular Mg17Al12 phases) and coarse grains (without Mg17Al12 phases) in the samples. The fine grains (with many granular Mg17Al12 phases) area expands with the decreasing of final forging temperature. The inhomogenous Al content distribution in the Mg matrix leads to the non-uniform dynamic precipitation of the Mg17Al12 phase. These Mg17Al12 phase retards the growth of the DRX grains, which in turns results in the formation fine grains area during the during the MDF process with temperature decreasing.

Effect of Combined Electromagnetic Fields on the As‐Casting Structure and Mechanical Property of HDC Casting 7075 Al Alloy Ingot

7075 Al alloy ingot with a diameter of 100 mm is produced by conventional and combined electromagnetic fields (CEMF) in horizontal direction chill (HDC) casting process. The effect of CEMF on the ingot as-casting structure and mechanical property is investigated. The results show that the CEMF is effective in refining the as-cast structure. Coarse feathery grains occupy the majority area of the cross section and the coarse equiaxed grains only distribute in a half-moon zoon near the bottom surface in the conventional HDC casting ingot. With the application of the CEMF, feathery grains mixed with exquiaxed grains only exist in a small area near the top surface, and fine equiaxed grains occupy the rest cross section. Tensile strength of the feathery grain structure is higher than that of equiaxed grain structure. The CEMF can make the mechanical property along the vertical direction of HDC casting ingot more uniform.

The effect of grain refiner and combined electro- magnetic field on grain evolution of horizontal direct chill casting 7075 aluminum alloy

Abstract The effect of increasing the amount of added grain refiner (Al-5Ti-B) and combined electromagnetic field on grain size and morphology has been investigated in horizontal direct chill casting of 7075 aluminum alloy. The results show the grain size and the grain morphology are both changed with increasing the amount of Al-5Ti-B added. The grain size continuously decreased with increasing the addition of grain refiner. The slope of the grain size versus grain refiner content curve changes at the point of 0.1 wt.% Al-5Ti-B, and the slope coefficient before the point is larger than that of after the point. The results related to the conglobulation of the nuclei. Without grain refiner additions, an obvious transition in grain size and morphology is observed with the application of combined electromagnetic field. The grain refining efficiency of combined electromagnetic field decreases with increasing the amount of grain refiner. However, even when the addition of grain refiner is 2 wt.% Al-5Ti-B, 24 % grain size reduction is still observed due to the effect of the combined electromagnetic field. This result shows that the combined electromagnetic field can enhance the grain refining efficiency of grain refiner.

Rapid air film continuous casting of aluminum alloy using static magnetic field

The influences of the cooling style and static magnetic field on the air film casting process were investigated. Ingots of 6063 aluminum alloy were produced by AIRSOL VEIL casting with double-layer cooling water and static magnetic field. Surface segregation, hot crack and variation of solute content along the radius direction of ingot were examined. The results showed that double-layer cooling water can improve the surface quality and avoid of hot crack, which created conditions to increase the casting speed. The electromagnetic casting process can effectively improve the surface quality in high speed casting process, and static magnetic field has a great influence on solute distribution along the radius direction of ingot.