Yong-lin Kang

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.

Microstructure and mechanical properties of rheo-diecasting AZ91D Mg alloy

Taking AZ91D magnesium alloy as experimental material, the rheo-diecasting process was implemented by combining the self-developed taper barrel rheomoulding(TBR) machine with high pressure die casting(HPDC) machine. Microstructural characteristics of the rheo-diecasting components were investigated in different processing parameters. Microstructural evolution and solidification behavior of the semisolid slurry during the rheo-diecasting process were discussed, and tensile properties of the components were studied as well. The results show that, with the rotation speed of the internal taper barrel increasing, the microstructure of the components becomes fine with solid particles nearly spherical and uniformly distributed on the matrix. When the rotation speed is 700 r/min, the primary α-Mg particles have an average size of about 45 μm and a shape factor of about 0.81; the primary α-Mg particles become round and homogeneous with shearing temperature increasing, but the average size is slightly larger. The solidification of the alloy melt during the rheo-diecasting process is composed of two distinct stages: the primary solidification and the secondary solidification. Compared with the conventional die-casting process, the rheo-diecasting process would improve the tensile properties of the components, especially the elongation by 80%.

Preparation of SiCp/A356 electronic packaging materials and its thixo-forging

Abstract The rapid development of electronic packaging industry has resulted in higher requirement for packaging materials. The packaging material of SiC reinforced A356 aluminum alloy was fabricated by mechanical mixing method, and the SiCp/Al composite billet was formed by thixo-forging to manufacture the electronic packaging shell. The microstructure of the produced part was investigated. Two different thixo-forging procedures for manufacturing electronic packaging shell were analyzed. The results show that after being heated to 600? and held for 3 h, SiC p has good compatibility with A356 aluminum alloy and the SiC p /A356 composite billet can meet the requirements of thixo-forging. When the billet was remelted to 580?, held for 10 min, the homogeneous microstructure with the best thixo-formability can be realized. The thixo-forging of electronic packaging shell is feasible.

Forced convection rheoforming process for preparation of 7075 aluminum alloy semisolid slurry and its numerical simulation

A self-developed forced convection rheoforming (FCR) machine for the preparation of light alloy semisolid slurry was introduced. The microstructure characteristics of 7075 aluminium alloy semisolid slurry at different stirring speeds prepared by the FCR process were analyzed. The experimental results suggest that with the increase of the stirring speed, the mean grain size of the semisolid decreases and the shape factor as well as the number of primary grains increase. Meanwhile, the preparation process of semisolid slurry was numerically simulated. The flow characteristics of the melt in the device and the effect of the stirring speed on temperature field and solid fraction of the melt were investigated. The simulated results show that during the preparation process of semisolid slurry, there is a complex convection within the FCR device that obviously changes the temperature field distribution and solid fraction of the melt. When the convection intensity increases, the scope of the undercooling gradient of the melt is reduced and temperature distribution is improved.

R-HPDC Process with Forced Convection Mixing Device for Automotive Part of A380 Aluminum Alloy

The continuing quest for cost-effective and complex shaped aluminum castings with fewer defects for applications in the automotive industries has aroused the interest in rheological high pressure die casting (R-HPDC). A new machine, forced convection mixing (FCM) device, based on the mechanical stirring and convection mixing theory for the preparation of semisolid slurry in convenience and functionality was proposed to produce the automotive shock absorber part by R-HPDC process. The effect of barrel temperature and rotational speed of the device on the grain size and morphology of semi-solid slurry were extensively studied. In addition, flow behavior and temperature field of the melt in the FCM process was investigated combining computational fluid dynamics simulation. The results indicate that the microstructure and pore defects at different locations of R-HPDC casting have been greatly improved. The vigorous fluid convection in FCM process has changed the temperature field and composition distribution of conventional solidification. Appropriately increasing the rotational speed can lead to a uniform temperature filed sooner. The lower barrel temperature leads to a larger uniform degree of supercooling of the melt that benefits the promotion of nucleation rate. Both of them contribute to the decrease of the grain size and the roundness of grain morphology.

Rheo-diecasting of AZ91D magnesium alloy by taper barrel rheomoulding process

Abstract A self-developed taper barrel rheomoulding (TBR) machine was introduced, and the rheo-diecasting process was implemented by combining TBR machine with the high pressure die casting (HPDC) machine. Microstructural characteristics of the rheo-diecasting components were investigated at different rotation speeds. Flow characteristics and microstructural evolution of the semi-solid slurry during the rheo-diecasting process were analyzed and the mechanical properties of the rheo-diecasting components were studied. The experimental results show that the process is able to obtain such components in which the primary α-Mg particles are fine, nearly spherical and uniformly distributed in the matrix. When the rotation speed of internal taper barrel is 700 r/min, the primary α-Mg particles get a mean diameter of about 45 μm and a shape factor of about 0.81. The magnesium alloy melt has complex stirring-fixed flow characteristics when flowing in TBR machine. Compared with conventional die-casing process, the rheo-diecasting process can improve the mechanical properties of components; especially, the elongation is improved by 80%.

Microstructure and properties of rheo-HPDC Al-8Si alloy prepared by air-cooled stirring rod process

Abstract A new and effective semisolid slurry preparation process with air-cooled stirring rod (ACSR) is reported, in which the compressed air is constantly injected into the inner cavity of a stirring rod to cool the melt. The slurry of a newly developed high thermal conductivity Al-8Si alloy was prepared, and thin-wall heat dissipation shells were produced by the ACSR process combined with a HPDC machine. The effects of the air flow on the morphology of α1-Al particles, mechanical properties and thermal conductivity of rheo-HPDC samples were studied. The results show that the excellent slurry of the alloy could be obtained with the air flow exceeding 3 L/s. Rheo-HPDC samples that were produced with the air flow of 5 L/s had the maximum UTS, YS, elongation, hardness and thermal conductivity of 261 MPa, 124 MPa, 4.9%, HV 99 and 153 W/(m·K), respectively. Rheo-HPDC samples show improved properties compared to those formed by HPDC, and the increasing rates of UTS, YS, elongation, hardness and thermal conductivity were 20%, 15%, 88%, 13% and 10%, respectively.

Taper barrel rheomoulding process for semi-solid slurry preparation and microstructure evolution of A356 aluminum alloy

Abstract The self-developed taper barrel rheomoulding (TBR) machine for light alloy semi-solid slurry preparation was introduced. The semi-solid slurry was obtained from the intense shearing turbulence of the alloy melt in the cause of solidification, which was further caused by the relative rotation of the internal and external taper barrel whose surface contained wale and groove. The heat transmission model of TBR process, the flow rules and the shearing model of the alloy melt were deduced. Taking A365 as experimental material, the microstructure evolution rules under different slurry preparation processes were analyzed. The results show that decreasing the pouring temperature of A365 alloy melt properly or increasing the shearing rate helps to obtain ideal semi-solid microstructure with the primary particle size of about 70 μm and the shape factor of above 0.8.

Effects of pouring temperature and cylinder temperature on microstructures and mechanical properties of rheomoulding AZ91D alloy

Abstract An advanced rheomoulder, which is a device in the integration of melting metal, storage, slurry preparation, transportation and injection forming, was introduced and used to manufacture rheomoulding AZ91D alloy. Effects of pouring temperature and cylinder temperature on microstructures and mechanical properties of rheomoulding AZ91D alloy were investigated. The results show that the process can obtain such rheomoulding AZ91D in which primary α-Mg particles are fine, spherical and uniformly distributed in the matrix. With the decrease of pouring temperature, the morphology of primary α-Mg particles changes from coarse rosette-like to fine spherical shape gradually. As the cylinder temperature decreases, the average size of primary α-Mg particles decreases firstly and then substantially maintains stable while the sphericity and solid fraction increase continuously. Also, decreasing pouring temperature or cylinder temperature properly contributes to improving mechanical properties of rheomoulding AZ91D for the refinement of α-Mg particles and the decrease of porosity fraction. Furthermore, rheomoulding AZ91D performs much better than thixomoulding, rheo-diecasting and high pressure die-casting (HPDC) in terms of mechanical properties. Compared with HPDC, the tensile strength, yield strength and elongation are increased by 27.8%, 15.7% and 121%, respectively.