Effect of Injected Oxygen Amount on the Gas Porosity and Mechanical Properties of a Pore-Free Die-Cast Al–Si–Cu Alloy

With the rise in the demand for eco-friendly and electric vehicles, welding and heat treatment are becoming very important to meet the necessary weight reduction, complexity, and high functionality of die castings. Pore-free (PF) die casting is an effective process that enables heat treatment and welding due to low gas porosities. Indeed, this process affords castings of low gas porosity, similar to those attained by high-vacuum die casting. In this study, we compared the gas porosities of different castings fabricated by PF die casting using varied injected oxygen amounts. The castings were all subjected to T6 heat treatment and analyzed by computed tomography (CT) to compare their microstructure and mechanical properties before and after T6 heat treatment. The results revealed that with the increasing injected oxygen amount, the gas porosity of the specimens decreased while their mechanical properties increased. In particular, the gas porosity was the lowest at 1.26 L. Moreover, the 1.26 L specimen displayed the best tensile strength, yield strength, and elongation results. Finally, Weibull distribution analysis revealed that the tensile strength and elongation repeatability and reproducibility increased with increasing injected oxygen amount.

Effect of Heat Treatment on Microstructure and Dimensional Stability of Y-Modified AlSi7Cu3Mg Alloy

The application of rare earth modified AlSi7Cu3Mg alloy in automobile engine and motor casing has increased. The dimensional stability of this alloy is an important feature. In this paper, the effects of yttrium addition and different heat treatment on the microstructure and dimensional thermal stability of AlSi7Cu3Mg alloy were studied by OM, SEM and dimensional measurement. Research shows that: The dimensional stability of AiSi7Cu3Mg alloy after T6 heat treatment is better than that after T4 heat treatment, and the dimensional stability after T7 heat treatment is the best. The addition of rare earth Y can improve the dimensional stability of AiSi7Cu3Mg alloy.

Effect of Short T6 Heat Treatment on the Thermal Conductivity and Mechanical Properties of Different Casting Processes Al-Si-Mg-Cu Alloys

The thermal conductivity of alloys is gradually becoming appreciated. It is often assumed that heat treatment can improve the thermal conductivity of Al-Si-Mg-Cu alloys, but there has been little relevant research. This paper studies the effects of different casting processes and short T6 heat treatment (ST6) on the thermal conductivity and mechanical properties of Al-Si-Mg-Cu alloys. The results show that a microstructure with fine α-Al crystal grains can be obtained by semi-solid die casting (SSDC), improving the mechanical properties of the Al-Si-Mg-Cu alloy in the as-cast state. After SSDC, the size and aspect ratio of eutectic silicon can be reduced by ST6 treatment, effectively improving the thermal conductivity and mechanical properties of the alloy. Finally, the influence of eutectic silicon on electron transport is analyzed in detail. With the SSDC + ST6 processing technology, Al-Si-Mg-Cu alloys with excellent thermal conductivity and mechanical properties can be obtained.

Al2O3 Particle Erosion Induced Phase Transformation: Structure, Mechanical Property, and Impact Toughness of an SLM Al-10Si-Mg Alloy

This study investigated the microstructure, mechanical properties, impact toughness, and erosion characteristics of Al-10Si-Mg alloy specimens manufactured using the selective laser melting (SLM) method with or without subsequent T6 heat treatment. Furthermore, the erosion phase transformation behavior of the test specimens was analyzed, and the effect of the degradation mechanism on the tensile mechanical properties and impact toughness of the SLM Al-10Si-Mg alloy specimens before and after particle erosion was compared. The experimental results indicated that the Al-10Si-Mg alloy subjected to T6 heat treatment has better erosion resistance than the as-fabricated material. The tensile strength and fracture toughness of both specimen groups decreased due to the formation of microcracks on the surface caused by particle erosion. Nevertheless, the erosion-induced silicon nanoparticle solid solution softens the Al matrix and improves the elongation of the SLM Al-10Si-Mg alloy.

Probability-Dependent Precipitation Strengthening Effect of Anisotropic Precipitate in Al-Mg-Si Alloy Produced by T6 Heat Treatment

This study proposed a constitutive equation to predict the change in yield strength according to the behavior of β″ metastable precipitates, which have a profound effect on strength among materials precipitated during the T6 heat treatment of Al-Mg-Si alloy. The β″ precipitate is a metastable phase before it becomes a β (Mg2Si) precipitate, and is distributed in the form of nano-scale rods in the aluminum alloy matrix. Existing precipitation strengthening models assume the shape of the precipitate to be spherical, and in that case the equation that depends on the Orowan mechanism with the average precipitate size and distribution should dominate. However, precipitates are formed in various shapes and sizes by anisotropic growth. In particular, rod-shaped precipitates are not suitable for the existing precipitation strengthening model. In this study, an Al-Mg-Si alloy was fabricated by gravity casting followed by T6 heat treatment. The new precipitation strengthening effect equation proposes that the β″ precipitate affects yield strength during plastic deformation of the Al-Mg-Si alloy. The proposed precipitation strengthening effect equation probabilistically considers the Critical Resolved Shear Stress (CRSS), which varies depending on the angle between the dislocation and the precipitate, when the dislocation passes through a rod-shaped precipitate.