The influence of heat treatment on the structure and tensile properties of thin-section A356 aluminum alloy casts refine
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ir Hosein Pourmonshi Department of Materials Engineering, Islamic Azad University, South Tehran Branch, Tehran 1777613651, Iran
Kourosh Tavighi School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, Tehran 1417614418, Iran (Received 22 February 2017; accepted 28 April 2017)
The aim of this study is to investigate the effects of different master alloys containing Ti, B, and Zr on the structure and tensile properties of thin-section A356 aluminum alloy in as-cast and T6-treated conditions. Microstructural examinations were performed using light optical and scanning electron microscopy. The results showed that the addition of 0.1 wt% Ti, 0.05 wt% B, and 0.1 wt% Zr decreases the average grain size of the cast alloy from 840 lm to 387 lm, 236 lm, and 363 lm, respectively. This structural refinement results in the variation of the a-Al primary phase distribution mode from dendritic to rosettelike. It has been found that 0.6 wt% Al–8B master alloy (0.05 wt% B) is the strongest to refine the structural parameters. This leads to the enhancement of both ultimate tensile strength and elongation values from 208 MPa and 6.2% in as-cast to 290 MPa and 12.5% in B-refined alloy at T6-treated conditions. In addition, the presence of more fine dimples on the fracture surfaces of the T6-treated specimens revealed that T6-treatment encourages ductile mode of fracture.
I. INTRODUCTION
A356 (Al–7% Si–0.3% Mg) is one of the most popular aluminum cast alloys which is widely used because of its attractive castability, heat treatability, and mechanical properties.1–4 Grain refinement is a critical operation in aluminum foundries that influences the quality of the cast parts.5–9 Chemical refinement of cast aluminum alloys has been applied for several decades10,11 and is currently become a routine practice in aluminum foundries. Titanium (Ti), boron (B), and zirconium (Zr) have been widely used in the form of different master alloys for grain refining of cast aluminum alloys.12–17 In late 1940s, the efficiency of grain refinement was considerably increased, when B was added to molten aluminum, allowing the same level of refinement at much lower Ti content.10 As a consequence, Al–Ti–B master alloys have been found as standard grain refiners for aluminum alloys ever since.12–15 Moreover, there are several references addressing the grain refining effects of Zr on cast aluminum alloys.17–20 Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.193
There are several accomplished works indicating the effects of applying different heat treatment procedures on A356 aluminum alloy.21–24 It is well established in the literature that during T6-treatment, the morphology of eutectic silicon particles changes from platelike to spherical in as-cast condition. This has a considerable influence on the mechanical properties, particularly, the ductility of the alloy. Although the automotive manufacturers demand for improved quality and properties, only few stu
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