Semi-solid Aluminum Alloy Research Articles

A study on solutions for avoiding liquid segregation phenomena in thixoforming process: Part II. Net shape manufacturing of automotive scroll component

The most important problem regarding the thixoforming process is the prevention of the liquid segregation phenomena during deformation. Since the liquid is of eutectic composition in materials, the liquid segregation will result in significant or undesirable situation. In this work, thus, the thixoforming experiments with a die designed to fabricate a net shape scroll component using semisolid aluminum alloys were carried out successfully. The die filling patterns of semisolid materials (SSMs) by varying the process parameters, such as die temperature and pressing force, have been investigated. The hardness and wear resistance of the thixoformed scroll product were evaluated in terms of both rheological and microstructural points of view. Two key features of the solutions that need to avoid the liquid segregation in the thixoforming process are the following. (1) It was concluded that to improve the thixoformability and to reduce the possibility of defects, the liquid segregation should be controlled as the multistage variation of the pressing velocity during forming. (2) In addition, the ability to model the material flow characteristics, including the solid/liquid segregation during die filling, will be required. This modeling technology is currently under development.

A study on solutions for avoiding liquid segregation phenomena in thixoforming process: Part I. Constitutive modeling and finite element method simulations for die design

The most important factor in the thixoforming analysis with die design is the relationship formulation between the stress and the strain considering the grain size and the deformation of the solid particles with a globular microstructure. In this present work, thus, a new stress-strain relationship formulation described as a function of the separation coefficient is proposed to consider the deformation of solid particles. Constitutive models are implemented by applying Darcy’s law for the liquid region and a porous media theory in the case of the solid region. A die designed to fabricate a net shape scroll component using semisolid aluminum alloys was performed using the finite element method (FEM). In the case of the solid fraction f s = 55 pct, the distributions of strain rate are calculated to assess the deformation behavior of semisolid materials (SSMs) by using the compression test data base of SSMs. By using these results, the effect of the overflow position in die design parameters on the liquid segregation in thixoforming process has been theoretically investigated.

K-0738 高固相率・半溶融アルミニウム合金の高速圧縮変形特性(S10-3 衝撃材料試験における新展開(3))(S10 衝撃材料試験における新展開)

Recently, semi-solid forming has been mainly utilized for automotive components such as the brake cylider. Semi-solid forming is a metal processing technique, which is becoming of large interest owing to many inherent advantages from a view point of saving energy, comparing with conventional forging (solid state) and casting (liquid state). In spite of the feasibility of semi-solid forming, its industrial application is limited. The faster forming speed tends to be required with complicating the figuration of compacts to attain the stable formability. It is noted that the applied uniaxial strain rate to materials is 10^2〜10^3 s^<-1> during forming. Very few data are, however, available concerning with the compressive behavior of semi-solid materials at a commercial forming rate. A classical Split Hopkinson Pressure Bar was used to estimate the dynamic mechanical properties of semi-solid aluminum alloy.

Mechanical properties and their microstructure evaluation in the thixoforming process of semi-solid aluminum alloys

Semi-solid forming technology has some advantages over conventional forming processes such as die casting, squeeze casting, and hot/cold forging. Thixoforging technology can produce non-dendritic alloys for the semi-solid forming of complex-shaped parts in metal alloys. In this study, the filling behavior and various defects of products were observed, and microstructures and mechanical properties were investigated along with parameters such as pressure and die temperature. Thixoforging experiments were performed at f s=55%. The punch speed was V d=200 mm/s. Die temperature was changed in steps to T d=400, 350, 300, and 250°C. The applied pressure was changed to P=100 and 150 MPa. The porosity, which is an internal defect, was observed, particularly at lower die temperatures. To distribute uniformly the regions of solid- and liquid-phase around the specimen on forming, it is necessary to increase the punch speed and optimize the gate design. Furthermore, a dense microstructure was found at lower die temperature and higher applied pressure. In a tensile test, it was observed that the higher the applied pressure, the higher the ultimate strength, yield strength, and elongation. In a hardness test, it was observed that the hardness decreased gradually from the center to the periphery of the specimen.

The induction heating process of semi-solid aluminium alloys for thixoforming and their microstructure evaluation

The optimal inductive coil design in the induction heating process of A356 (ALTHIX) alloy billets of 76 mm diameter and 90 mm length to reduce the temperature gradient of the billet and to obtain a globular microstructure was theoretically proposed and tested by reheating experiments. The optimal reheating conditions to apply the thixoforming process were investigated by changing the reheating time, holding time, holding temperatures, capacity of the induction heating system, and adiabatic material size. This study shows that, the larger the billet size, the better the multi-step reheating, and the heating time and the capacity of the induction heating system must be increased. In case of the three-step reheating process, the final holding time is most important factor and 2 min is suitable to maintain a globular microstructure.

The effect of strain rate on macroscopic behavior in the compression forming of semi-solid aluminum alloy

Abstract The behavior of alloys in the semi-solid state depends strongly on the imposed stress state and the morphology of the phase, which can vary from dendritic to globular. For the optimal net shape forging of semi-solid materials (SSM), it is important to have knowledge of the material behavior with variation of strain rate. Therefore, to investigate the effect of the compression velocity of the deformation of aluminum alloy with a globular microstructure, the compression test for semi-solid aluminum alloy with a controlled solid fraction is performed by material test system provided with a furnace. The behavior of the semi-solid aluminum alloy is discussed for various solid fractions and die speeds. The material constants in the stress–strain relationship are also proposed.

アルミニウム鋳造の最新技術 アルミニウム合金の半凝固・半溶融加工法

アルミニウム鋳造の最新技術 アルミニウム合金の半凝固・半溶融加工法

Solidification of aluminium spray-formed billets

A critical part of the billet spray-forming process is the successive intermittent deposition of thin layers of semi-solid aluminium alloy at different points on the top surface of the billet. Each thin layer is made up of a large number of impacted semi-solid spray droplets. As successive layers of alloy are deposited significant re-melting and re-freezing of underlying layers can occur. If the layers become too dry, high porosity will result; if they are too wet, fluid dynamic surface instabilities are possible. In extreme cases no billet will form. The process is essentially incremental, so that heat fluxes within the deposit very close to the top surface play a major role in determining the final deposit microstructure.

A Compression Behavior of Semi-Solid Material and Finite Element Analysis Considering Flow of Liquid Phase

Compression behavior of semi-solid aluminum alloys with controlled solid fractions was investigated in the present study. The stress and strain relationships were obtained from the compression test. Variations of the solid fraction distribution and the material behaviour were investigated for various friction coeffieiants and die speedsd. For a finite element analysis, the semi-solid material was described by a compressible regid viscoplastic model for the solid region and darcy's law for the liquid region. The computed results were compared with experimental data for the validity of the yield criteria.

Properties of Semi-solid Aluminum Alloy Castings Made by High Pressure Casting Process

Properties of Semi-solid Aluminum Alloy Castings Made by High Pressure Casting Process

Migration of particles during extrusion of metal matrix composites

Migration of particles during extrusion of metal matrix composites

Castability of Pasty Semi-Solid Aluminum Alloy into Shell Mold

Castability of Pasty Semi-Solid Aluminum Alloy into Shell Mold