Abstract
The effects of heat treatment on the microstructural evolution and mechanical behavior of Al-Si-Cu alloy were investigated. Solution heat treatment was performed at 500oC/6h and 540oC/6h, followed by quenching in warm water at 60ºC. Lastly, artificial ageing treatment was performed at 160ºC/6h, 190ºC/4h and 210ºC/2h. The microstructural evolution of the samples before and after heat treatments was analyzed by optical microscopy, scanning electronic microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). Analyses revealed the presence Al5FeSi, Al15(FeMn)3Si2, Al2Cu and Si particles. The morphologies of the present phases were dependent on the heat treatment. Solution treatment at 540ºC/6h resulted in significant softening of the alloy compared with the treated samples at 500ºC/6h. Vickers hardness analysis indicated that the hardness peak of the alloy after heat treatment was about 125 HV. Mechanical properties of different phases have been investigated by nanoindentation technique, which indicated that the highest hardness and modulus of elasticity were found for the Si particle, especially those distributed in the microstructures of the samples submitted to higher solution and ageing temperatures.
Highlights
The hypoeutectic Al-Si-Cu alloys present excellent mechanical properties, including a good strength versus weight ratio, which make these alloys excellent choices for automotive industries[1]
- As-cast Al-Si alloy revealed a microstructure composed of primary dendritic α-Al matrix grains, along with Al-Si eutectic region as well as Al5FeSi, Al15(FeMn)3Si2 and Si particles distributed on the α-Al matrix
- Microhardness tests showed an increase of vickers hardness in all treated samples for both solution treatment and ageing; higher hardness valeus were found for ageing treatments performed at 190oC/4h
Summary
The hypoeutectic Al-Si-Cu alloys present excellent mechanical properties, including a good strength versus weight ratio, which make these alloys excellent choices for automotive industries[1]. The Al-Si-Cu alloys in the as-cast condition present microstructures composed by primary aluminum matrix with predominantly dendritic grains and Al-Si eutectic region[2]. The presence of elements as Fe, Cu, Mg and Mn in their chemical composition may promote the formation of intermetallic compounds as Al5FeSi, Al15(FeMn)3Si2 and Al2Cu on the microstructures of the aluminum alloys[3]. Some intermetallics may be responsible for decreasing the mechanical properties on the materials. Some of Fe-rich compounds present needle-shaped morphology, which may cause material embrittlement by stress concentration[4]. The presence of Al2Cu and Al15(FeMn)3Si2 on the microstructure, promotes a good combination of strength and ductility in the alloys[5]
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