Hot Processing Maps and Microstructural Characteristics of A357 Alloy
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Hot Processing Maps and Microstructural Characteristics of A357 Alloy Fuwei Kang, Shijie Wei, Jimin Zhang, Enhao Wang, Dezhi Fan, and Shanshan Wang (Submitted June 6, 2019; in revised form September 8, 2020; Accepted September 20, 2020) In this paper, the hot deformation behavior of A357 alloy was investigated by hot compression tests. Isothermal hot compression simulation tests for A357 alloy were carried out at the conditions of deformation temperature of 350-470 °C, strain rate of 0.001-10 s21 and engineering strain of 50%. Based on the Prasad instability criterion and dynamic material model, the hot processing maps of A357 alloy were constructed. The microstructure of compressed samples at different areas of the hot processing map was characterized by metallographic and scanning electron microscope and transmission electron microscope. The experimental results showed that the unstable processing zone of A357 alloy was mainly distributed in the high strain rate (10 s21) and low-temperature (350, 380 °C) region. With an increase in the strain, the unstable zone expanded from low temperature to high temperature (470 °C). The ideal deformation conditions were deformation temperatures of 380-410 °C and strain rates of 0.001-0.01 s21, and deformation temperatures of 440-470 °C and strain rates of 0.01-1 s21. When the A357 alloy was extruded with the optimal hot processing parameters, the results suggested that hot extrusion could make the microstructure uniform and fine, thereby improving mechanical properties, especially when the elongation was up to 19.5% higher than the as-cast A357 alloy. Keywords
A357 alloy, hot processing map, microstructure, mechanical properties
1. Introduction As an age-hardened aluminum alloy, A357 alloy is widely used in aviation, aerospace and automotive industries because of its excellent castability, weldability and hot-cracking resistance (Ref. 1, 2). However, coarse eutectic Si particles and AlFeSi-based intermetallic phases in the casting process may limit the application of the alloy. These problems inherent in the casting process can be improved by degas, degeneration treatment and hot working, which bring about a significant microstructural modification of this alloy in size, morphology and distribution of Si particles as well as the intermetallic compounds (Ref. 3-6). Among the preceding techniques, hot working was one of the long-established and important production methods. Appropriate selection of hot working parameters critically affects the microstructure and properties of the productions or components, and hot processing maps are an effective way to solve this problem (see 3.2 part). For A357 alloy, it is interesting to investigate its hot deformation characteristics, and the extensive works are carried out on casting technique, heat treatment, microstructure and mechanical properties aspects (Ref. 7-12).
Fuwei Kang, Shijie Wei, Jimin Zhang, Enhao Wang, Dezhi Fan, and Shanshan Wang, School of Materials Science and Engineering, Harbin Uni
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