Comparisons of Age Hardening and Precipitation Behavior in 7075 Alloy Under Single and Double-Stage Aging Treatments
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Comparisons of Age Hardening and Precipitation Behavior in 7075 Alloy Under Single and Double‑Stage Aging Treatments Yun Fan1 · Xuan Tang2 · Shaohan Wang1 · Bin Chen1 Received: 17 May 2020 / Accepted: 2 September 2020 © The Korean Institute of Metals and Materials 2020
Abstract Various sets of heat treatments are applied on 7075 alloy in this study in order to reduce the treatment time and yet still achieve the similar mechanical property as the traditional T6 tempered alloy. The main parameters like solid solution treatment time, single aging temperature, as well as first aging duration in double aging treatment, first aging temperature and second aging temperature are studied and valued by hardness test. The double aging treatment at 125 °C for 60 min and then at 165 °C for 130 min is compared with traditional single aging treatment by using advanced Cs-corrected high-angle annular dark field scanning-transmission electron microscopy (HAADF-STEM). The precipitates and dispersoids found in those two corresponding samples are mainly Cr-containing large dispersoids, a few η particles and large quantity of fine precipitates like η′. The similarity of precipitates in them can well support the approximate hardness level of the double aged and single aged samples. Keywords 7075 Alloy · Double Aging Treatment · Hardness · Precipitate · Dispersoid
1 Introduction In order to respond to the urge of energy saving and emission reduction, the demands for lighter materials are increased in the automotive industry. Studies showed that 6%–8% petrol consumption and 4%–6% CO2 emission can normally be reduced by a car mass reduction of 10% [1, 2]. Materials like aluminum alloys, ultra-high strength steels, composite materials and other light alloys such as magnesium alloys and titanium alloys have huge potential of rendering vehicles lighter. However, when considering the factor of costs and security, only high strength aluminum alloys and steels remain as the main focus of achieving the weight-loss goal. Moreover, to obtain the high strength-weight ratio, many high strength steels are designed to be boron martensite steels which suffer the inevitable embrittlement caused by hydrogen, making them less tough and their applications limited [3]. Therefore, promoting the use of aluminum * Bin Chen [email protected] 1
School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
Department of Vehicle Engineering, NIO Co. Ltd, Shanghai 201814, China
2
alloys, especially in the car body parts, can be a suitable approach of lowering car mass. According to an investigation in 2010, about 140 kg aluminum alloys are used in a vehicle in the U.S., 80% of which are cast parts such as engine block and wheels, while the aluminum sheets are hardly used [1]. Therefore, developing the aluminum sheets applications might invoke great weight loss of a car, which draws attention to Al-Zn-Mg-Cu alloys because of their appealing strength-weight ratio, their better toughness comparing to high strength
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