Abstract
In the present investigation, Al-(20-30%wt) Mg2Si-2Cu alloys were synthesized by spray forming process and further processed by hot pressing for densification. The alloys were further subjected to age hardening heat treatment. The spray formed, age hardened and as-cast alloys were characterized by microstructure and mechanical properties. The microstructure of spray formed alloys exhibited finer and evenly distributed primary β-Mg2Si particles and θ-Al2Cu phase and clusters of discrete and high volume fraction of Q-phase. As-cast alloys mainly consist of large sized polygonal primary β-Mg2Si, coarse Chinese script of Al2Cu and needle shaped eutectic Q-phase. Hot pressing of the spray formed alloy promotes the microstructural refinement, reduction in porosity, fragmentation and redistribution of secondary phases. Artificial age hardened alloys exhibits the large quantity of θ-Al2Cu precipitates less than 2 μm size uniformly distributed in the matrix. The β phase re-precipitates in a very fine spherical form results in an increase in the area fraction of β-Mg2Si phase during aging. The significant enhancement in ultimate strength in heat treated and sprays formed alloys as compared to the as-cast alloy. The SEM of fracture surfaces of tensile specimens was taken on spray formed age hardened and as cast alloys. The fractographs revealed the transformation from brittle mode to ductile dimples.
Highlights
The hypereutectic Al-Si alloys with alloying elements such as Mg, Cu, Fe and Mn have been successfully produced by modern processing technologies to improve strength to weight ratio, mechanical properties and wear behavior at elevated temperature [1]
The strongest diffraction peak of primary Mg2Si phase of spray forming (SF) alloy corresponds to the (220) plane. This indicates the crystalline growth of primary Mg2Si phase in SF alloy
The increase in the hardness of SF+HP alloy is due to the partial recrystallization, fragmentation and redistribution of primary Mg2Si phase, precipitation of fine θ, Q phases and reduced porosity due to hot pressing
Summary
The hypereutectic Al-Si alloys with alloying elements such as Mg, Cu, Fe and Mn have been successfully produced by modern processing technologies to improve strength to weight ratio, mechanical properties and wear behavior at elevated temperature [1]. Large amount of fine, uniformly distributed primary Mg2Si particles and greater number of precipitates (θ-Al2Cu phase, Q phase) are formed in the supersaturated Al-matrix. The increase in the hardness of SF+HP alloy is due to the partial recrystallization, fragmentation and redistribution of primary Mg2Si phase, precipitation of fine θ, Q phases and reduced porosity due to hot pressing.
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