The relationship between the process parameters and the mechanical properties of injection molded magnesium alloys based on Mg–Al system (AZ91D, AM60B, AM50A and AS41B) is investigated. It is shown that the tensile properties of injection molded specimens are superior to those of die casting. A high barrel temperature reduces solid fraction and improves tensile properties of injection molded magnesium alloys. These properties tend to saturate above the liquid temperature.

View full abstract

Extruded sections of aluminum have many advantages for lightweight structural members. A secondary forming process, such as bending, is required when these materials are used in these parts. In this paper, we investigated deformation property of tension-side open type 6063 aluminum alloy extruded sections in the rotary draw bending process. A6063S extruded sections having various thickness applied to the workpiece of this experiment. In the rotary draw bending process of these workpieces, undesirable phenomena such as flattening distortion, compression flange wrinkling and web wrinkling arise in the same way as square tube. Flattening distortion can be restrained principally by rigid mandrel and restriction guide for web displacement. Compression flange wrinkling can be restrained by additional axial tension. As a result of this study, it has been shown that applying these restriction tools and additional axial tension are very effective in preventing undesirable deformations. The bend degree H₀/R₀ reaches 0.24 without any defects in this bending process, the workpiece of A6063S–O with thickness ratio H₀/t₀ = 26.7.

View full abstract

The purpose of this study is to improve the hardness and wear resistance characteristics of the aluminum alloy using Plasma Transferred Arc process, called PTA process. The PTA process has been mainly applied to surface modification to steel products. It has some difficulties to apply this PTA process into aluminum products due to its low melting point and high thermal conductivity. It can be possible to make stable surface modification to aluminum alloy optimizing plasma current and powder supply. Niobium carbide powder was selected to obtain the optimum hardness and wear resistance during a series of experiments using PTA process. As the conclusions, sufficient hardness and wear resistances were archived at the surface modified layer by controlling niobium carbide composition to aluminum powder in the PTA deposit metal. Deposits which have no blowhole, crack and detachment from base metal were obtained in case of more than 60%NbC content of mixture ratio.

View full abstract

Microstructures, Vickers hardness, tensile properties and rotated beam fatigue properties of friction welded aluminum-borate whisker reinforced Al–Cu alloy matrix composites (MMC) joints with Al–Si–Cu–Mg alloy (C355) castings were examined. The mixed layer of MMC and C355 is formed near the bonding interface by the shear stress during the rotated friction period. This layer has different composition from both Al–Cu alloy and Al–Si–Cu–Mg alloy, and the mixed layer has lower strength but also has a role to relax thermal stress during water-quenching after solution treatment. Softening occurs near the bonding interface and the joints have lower tensile properties than those of C355 alloy castings in as-friction welded joints. After T6 heat treatment, hardness of the joint is recovered and the joint has higher tensile and fatigue properties than those of C355–T6 alloy castings. It is concluded that a combination of the friction welding and post-weld T6 heat treatment is a reliable method to assure good performance for MMC/C355 joints.

View full abstract

Fatigue crack propagation characteristics of a eutectic and two hypereutectic Al–Si–Cu die casting alloys were investigated, where the stress ratio was 0.1 and the load frequency was 50 Hz at an ambient temperature. Relationships between fatigue crack propagation characteristic and microstructure have been dicussed. The fatigue crack propagation rate decreases with increasing Si content in a low stress intensity factor range, ΔK. In this range, the crack propagation rate is very slow because it is considered to increase effects of crack deflection and branching induced crack closures with increasing Si content. At a high ΔK, because the effects of crack closures are decreased, the higher the Si content, the higher the fatigue crack propagation rate becomes. In this study, the fatigue crack propagation rate for the Al–15%Si–T5 alloy becomes higher than the other two alloys. It is considered to decrease effects of crack deflection and branching induced crack closures with many intermetallic compounds in the Al–15%Si–T5 alloy. The fractographic study on fractured specimens after fatigue crack propagation tests reveals the fracture surfaces consisting of the cleavage fractures of Si and intermetallic compound particles, and the striation pattern in α–aluminum.

View full abstract