The Impact of Solution Treatment Time (T6) and Deep Cryogenic Treatment on the Microstructure and Wear Performance of Ma
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JMEPEG https://doi.org/10.1007/s11665-020-05058-4
The Impact of Solution Treatment Time (T6) and Deep Cryogenic Treatment on the Microstructure and Wear Performance of Magnesium Alloy AZ91 Mustafa O¨zgu¨r O¨teyaka
, Burak Karahisar, and Hasan Candan O¨teyaka
(Submitted March 5, 2020; in revised form June 1, 2020) In this study, the AZ91 magnesium alloy was subjected to solution and ageing heat treatment (T6) and deep cryogenic (DC) treatment to enhance the wear performance. For this purpose, the solution treatment process was performed at 400 °C for 4 h, 5 h, and 6 h, followed by ageing at 200 °C for 10 h to complete T6 treatment. Then, the DC treatment was carried out at 2 196 °C for 48 h. The pin-on-disc method was employed to measure the wear resistance of the samples. The results show that the solution treatment period altered the microstructure of AZ91; the eutectic phase was more dissolved in the matrix after 4 h of solution treatment time. Regarding the DC-treated AZ91, new double twins frame-like b phases were observed on the surface. Moreover, cryogenic treatment improved the hardness from 63 to 75 HV, but the wear rate was slightly higher than untreated AZ91 in dry medium. On the other hand, lower wear rate was obtained when applying 4 h of solution treatment time with DC treatment. In contrast, 6 h of solution treatment time with DC treatment exhibited higher wear rate, probably due to greater amounts of double twins. Keywords
AZ91, ageing, deep cryogenic, heat treatment, magnesium, wear
1. Introduction Magnesium alloys containing aluminum and zinc as principal alloy elements have become more prominent in the industry, and they are expected to replace aluminum alloys soon. The main advantage of magnesium alloys compared to other materials is their low density and high specific strength ratio. Their primary usage area is the automotive and transportation industry because of their weight efficiency and potential to save fuel consumption (Ref 1-3). The most popular casting method for magnesium alloys is high pressure die casting (HPDC). On the other hand, gravity sand and permanent mold casting are used for high-performance aerospace and defense parts (Ref 4). Among AZ series, the AZ91 alloy is one of the most popular magnesium alloys due to its good castability, strength and ductility. In general, AZ91 alloy contains a-Mg matrix, a + b eutectic, and b intermetallic phases in its microstructure. The quantity and distribution of the phases vary depending on production methods. The disadvantages of AZ91 are poor corrosion performance in a saline environment, medium mechanical properties, insufficient duc-
¨ zgu¨r O ¨ teyaka, Eskis¸ ehir Vocational School, Eskis¸ ehir Mustafa O Osmangazi University, Eskis¸ ehir, Turkey; Burak Karahisar, Aerospace Science and Technology, Eskis¸ ehir Osmangazi University, ¨ teyaka, Department of Eskis¸ ehir, Turkey; and Hasan Candan O Mechanical Engineering, Faculty of Engineering, Dumlupınar University, Ku¨tahya, Turkey. Contact e-mails: [email protected], karahisarburak@g
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