Zhan-yong Zhao

Fabrication of AZ31 alloy wire by continuous semisolid extrusion process

Abstract A novel technology of continuous semisolid extrusion Process (CSEP) was adopted to produce AZ31 alloy structural materials. Effects of technological conditions on the microstructures of AZ31 alloy during CSEP were studied. During the casting process, the non-uniform distribution of microstructures was found in the roll-shoe gap. Microstructure evolution from dendrite to rosette or spherical grains was observed during the casting process by CSEP. The results show that high casting temperature and large cooling intensity can cause non-equilibrium solidification region near the roll surface, large roll-shoe gap width and high cooling intensity can lead to the formation of discontinuous solidification microstructure and slip plane near the shoe surface, which will finally cause the failure of the casting process. The proper casting temperature range of 730–750 °C, the roll cooling intensity of 0.4 L/s and the roll-shoe gap width of less than 10 mm are suggested. Under the suggested conditions, the product with diameter of 10 mm of AZ31 alloy with smooth surface and homogeneous striped microstructure is obtained. The average strength of the product after heat treatment reaches 270 MPa, and the elongation is 16%.

Effects of technical parameters of continuous semisolid rolling on microstructure and mechanical properties of Mg-3Sn-1Mn alloy

Abstract A sloping semisolid rheo-rolling process of Mg–3Sn–1Mn alloy was developed, and the effects of process parameters on the microstructure and mechanical properties of Mg–3Sn–1Mn alloy strip were studied. The results show that the primary grain average diameter of the strip increases with the increase of the roll speed. The primary grain average diameter decreases firstly and then increases with the increase of the vibration frequency, and the tensile strength and elongation of the strip increase firstly and then decrease with the increase of the vibration frequency. The primary grain average diameter increases with the increase of casting temperature, and the tensile strength and elongation of the strip decrease correspondingly. When the casting temperature is 670 °C, the roll speed is 52 mm/s, and the vibration frequency is 60 Hz, Mg–3Sn–1Mn alloy strip with good properties is produced. The mechanical properties of the present product are higher than those of Mg–3Sn–1Mn alloy casting with the addition of 0.87% Ce (mass fraction).

Effect of Wavelike Sloping Plate Rheocasting on Microstructures of Hypereutectic Al-18 pct Si-5 pct Fe Alloys

To refine and spheroidize the microstructures of hypereutectic Al-Si-Fe alloys, a novel method of wavelike sloping plate (WSP) rheocasting was proposed, and the effect of the WSP rheocasting on the microstructures of hypereutectic Al-18xa0pct Si-5xa0pct Fe alloys was investigated. The results reveal that the morphologies of the primary Si crystal, the Al18Si10Fe5, and the Al8Si2Fe phases can be improved by the WSP rheocasting, and various phases tend to be refined and spheroidized with the decrease of the casting temperature. The alloy ingots with excellent microstructures can be obtained when the casting temperature is between 943xa0K and 953xa0K (670xa0°C and 680xa0°C). During the WSP rheocasting, the crystal nucleus multiplication, inhibited grain growth, and dendrite break-up take place simultaneously, which leads to grain refinement of the alloys.

Microstructure evolution and solidification behaviors of A2017 alloy during cooling/stirring and rolling process

A novel semisolid rheo-rolling process of A2017 alloy was achieved by combining the shape rolling mill with the vibrating sloping plate device. The microstructure evolution and solidification behaviors during the process were investigated. The high cooling rate caused by the sloping plate and stirring action caused by the vibration and metal flow lead to a high nucleation rate as well as two primary grain growth patterns, direct globular growth as well as dendrite growth and subsequent breakage, which causes the formation of fine spherical or rosette primary grains. During the rolling process, the grains of the strip were elongated. The primary grain size of A2017 alloy strip increases with the increment of casting temperature. When the casting temperature was between 650 °C and 660 °C, A2017 alloy strip with good quality was produced by the proposed process. The microstructures of the strip are mainly composed of spherical or rosette grains.

Simulation of temperature field and metal flow during continuous semisolid extending extrusion process of 6201 alloy tube

Abstract A continuous semisolid extending extrusion (CSEP) method was proposed. Temperature field and metal flow during continuous semisolid extending extrusion process of 6201 alloy tube were studied. During the process, the temperature in the roll-shoe cavity decreases gradually, and the isothermal lines of the alloy deviate from the shoe side to the work roll side in the roll-shoe gap. Metal flow velocity decreases gradually from the surface of the work roll to the surface of the shoe. In the extrusion mould, alloy temperature decreases gradually from the entrance to the exit and from the center to the sidewall of the mould. The extending cavity is radially filled with the alloy. The flow lines in the tube corresponding to the centers of the splitflow orifices and the welding gaps are dense, and the corresponding harness values are high; there are 8 transitional bands between them. In order to prepare 6201 alloy tubes with good surface quality, the pouring temperature from 750 °C to 780 °C was suggested.

Metal solidification–nucleation–rate model under coupling effects of shearing flow and vibration

This paper proposes the influence factors of coupling effects of shearing flow and vibration on diffusion coefficient and critical nucleation energy during metal solidification. Based on this proposal, a metal solidification–nucleation–rate model under coupling effects of shearing flow and vibration is established. Verification experiment using Al–7Si alloy is carried out. When vibration frequency and melt flow velocity are zero, the results calculated by the above model agree with that calculated by Turnbull’s theory. The results calculated by the above model under coupling effects of shearing flow and vibration agree with the experimental results, with the error within 0·2–14·3%. So the established model can calculate and explain the nucleation rate of melt under coupling effects of shearing flow and vibration.

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.

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.

Mathematic model of rolling pressure during a semisolid shearing-rolling process

A mathematic model of rolling pressure during a novel semisolid shearing-rolling process was established. The rolling pressure in this process is higher than that in the conventional rolling. The increment of rolling pressure in the backward slip zone is higher than that in the forward slip zone, and the neutral plane moves toward to the roll gap entrance. The maximum and the average rolling pressures increase with the decrease of strip thickness, and the effects of strip thickness on the rolling pressure is more obvious in the forward slip zone than in the backward slip zone. Meanwhile, the neutral plane moves toward the roll gap exit with the decrease of strip thickness. The maximum and average rolling pressures increase with the decrease of strip width, and the strip width affects the pressure more obviously in the backward slip zone than in the forward slip zone. At the same time, the neutral plane moves toward the roll gap entrance with the decrease of strip width. The maximum and average rolling pressures increase with increasing roll radius, and the neutral plane moves toward the roll gap exit.