Papers by Keyword: Aluminum Cast Alloy

Abstract: This study focuses on the role of Mo addition on the mechanical properties of an Al-Si-Cu-Mg alloy in as-cast and heat-treated condition at ambient and elevated temperature. Addition of 0.4 to 0.6 wt.% Mo forms Mo-bearing dispersoid particles which have a relatively high melting point and improve high temperature tensile strength. Ductility suffered in the presence of Mo-bearing particles. Trace addition of Mo up to 0.6 wt.% has a negligible influence on the yield strength and hardness of Al-Si-Cu-Mg alloy in as-cast and heat-treated conditions at ambient temperature and 250 °C.

Abstract: Tribological properties of textured surfaces fabricated using a discontinuous microcutting process were investigated. Aluminum cast alloy (AC8A) discs were used for the specimens. The texturing process was carried out using a CNC machining center with a cutting edge with a novel geometry. The resulting surface morphology consisted of micro dimples with a diameter of 200-300 μm and a depth of 5-10 μm, with controlled area fractions of 10 and 40% and a top region finished with a milling cut. The tribological properties were evaluated using a ring-on-disc type testing apparatus under lubricated conditions, and showed that the friction coefficient of the textured surfaces was low and stable from the beginning of the experiment. A dependence of the friction coefficient on the area fraction was also found. Further reductions in the friction coefficient were achieved on a textured surface with a polished top region. It can be concluded that the proposed discontinuous micro cutting process is an effective means of fabricating a micro texture for the reduction and stabilization of frictional resistance.

Abstract: The correlation between the microstructure, the mechanical properties and the fatigue life of the common aluminum cast alloy Al-7Si-0.3Mg (A356) was investigated. By variation the solution heat treatment temperatures and times the precipitation strengthening effect in the dendritic aluminum solid solution phase and the spheroidization of the eutectic silicon were modified. The results of fully reversed fatigues tests revealed an increase in the fatigue life of specimens that were heat treated at higher temperatures. This observation was supported by analyzing the fatigue crack propagation behavior using the direct current potential drop technique (DCPD). With (i) increasing heat treatment temperature, i.e., increasing dendritic α-Al strength and (ii) roundness of the eutectic silicon particles the resistance to technical fatigue crack initiation, expressed by the threshold value of the stress intensity range K_th, was shifted to higher values.

Abstract: According to the principle of bubble floatation, purification of ZL114 aluminum casting alloy has been studied by blowing nitrogen gas into the ZL114A alloy melt through the porous plug which can produce dispersed micro bubbles. 5 samples have been taken at 0 min, 2 min, 4 min, 6 min, 8 min and 10 min, respectively, to measure the hydrogen content through HYSCAN II hydrogen tester. The experiments results show that the removing effect of hydrogen is remarkable. The hydrogen removing efficiency reaches 85.7% when blowing lasts 4 minutes. The rate of hydrogen removing begins to decrease from 4 minutes to 10 minutes; the hydrogen removing efficiency gets to the maximum after 8 minutes. The inclusions are also removed with the removal of hydrogen.

Abstract: Specimens of the common cast alloy Al-7Si-0.3Mg (A356) were solution heat treated at different temperatures and times to modify (i) the precipitation strengthening effect in the aluminum solid solution phase and (ii) to spheroidize the eutectic silicon. Just 15 minutes of solution heat treatment at a temperature of 540°C are sufficient to reach the desired effect. Cyclic loading experiments revealed an increase in fatigue life as compared to specimens heat treated at lower temperatures. In particular in the HCF regime, fatigue cracks that were originally initiated at pores follow crystallographic slip bands under shear control (mode II) as it was proven by automated EBSD (electron back scatter diffraction) measurements. The smoothly polished surface of the fatigue specimens was observed continuously by a long-distance microscope and discontinuously by SEM (scanning electron microscopy) to identify the fatigue crack propagation mechanisms. It was shown that da/dN decreases strongly when the crack tip interacts with the eutectic areas. Obviously, the blocking effect of the eutectic silicon particles makes the crack leaving the straight slip-band path.

Abstract: Effect of plant oil on the fatigue strength of a squeeze cast Al-Si-Mg alloy was investigated. Crack growth rate was higher in plant oil than in air, inducing a decrease in fatigue strength. The reason included is explained from the viewpoint of high water absorbency of plant oils, on basis of hydrogen enhanced localized plasticity.

Abstract: The correlation of age hardening behavior and Si precipitation in α(Al) of Al-8wt%Si-0.35wt%Mg alloy has been investigated by micro hardness measurement, electron probe microanalysis (EPMA) and transmission electron microscopy (TEM) analysis. The EPMA results show that Si concentration in the center of α (Al) dendrites is higher than that in the edge and the main concentration is about 1.5wt% for Al-8wt%Si-0.35wt%Mg alloy in as cast condition. After solution treatment at 530 °C for 8 h followed by water quenching (T4 treatment), hardness value decreases 9 HV, which is accompanied by the decrease of Si concentration in α (Al). Aging the as-cast sample and T4 treatment sample at 150 °C for 20 h, the main concentration of Mg and Si in α (Al) changes little. Hardness value after as-cast aging is only 3 HV lower than that after T6 treatment. Nanometer Si particles and β″ and/or β′ phases are found in aged samples. The higher hardness value for as-cast aging samples should contribute to the nanometer Si particles in α (Al).

Abstract: The aging hardening behaviors of Al-8Si-3%Cu (wt%) and Al-3Cu (wt%) alloys have been investigated. Samples were solution treated at 500 for 24 h followed by water quenching before aging. Hardness has been measured for quenched samples aging at 150°C. Strong age hardening occurs for Al-3Cu alloy and hardness increases by about 60% after peak aging. There is a hardness decrease in the early aging stage of Al-8Si-3Cu alloy and hardness increases by about 15% after peak aging. The age precipitation behaviors have been analyzed using DSC and TEM. Effects of microstructure characteristics on age precipitation and age hardening response of Al-8Si-3Cu alloy have been discussed.