A study of the mechanical properties of a Mg-Al-Zn alloy (AZ91) produced via Thixomolding
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ORIGINAL RESEARCH
A study of the mechanical properties of a Mg-Al-Zn alloy (AZ91) produced via Thixomolding Mitsuhiro Okayasu 1 & Takahiro Fukui 1 Received: 28 April 2020 / Accepted: 9 September 2020 # Springer-Verlag France SAS, part of Springer Nature 2020
Abstract In this work, the mechanical properties and failure characteristics of a Mg-9.0Al-0.8Zn alloy (AZ91) fabricated via the Thixomolding process (TC) were investigated and compared with those of alloys formed via other casting processes, including cold-chamber die-casting (CD) and hot-chamber die-casting (HD). The microstructure of the three cast samples mainly consisted of the α-Mg phase and eutectic Mg17Al12. Fine, uniformly organized spherical α-Mg grains formed in the TC sample, and this morphology can be related to the TC process. A relatively small microstructure, comparable to the TC sample, was also obtained with CD because of the high solidification rate. However, large grains and cast defects were observed in the HD sample. Shrinkage porosity cast defects were dominant with HD, and they were caused by the low casting pressure. The ultimate tensile strength and 0.2% proof stress of the TC sample were 279 MPa and 192 MPa, respectively, which was ~10% higher than for the CD sample. The cast defects and large grains for the HD sample caused a significant reduction in its tensile properties, although its 0.2% proof stress was relatively similar to the CD sample. High fatigue strength and high crack growth resistance were realized with TC. Failure analysis was also carried out to probe the excellent mechanical properties of the TC sample. Keywords Die-casting . Thixomolding . Mechanical property . Microstructure . Magnesium alloy
Introduction Magnesium alloys are attractive materials because of their light weight and high strength-to-weight ratio [1], and they have been used in the automotive and aerospace application opportunities to address energy and environmental concerns [2, 3]. Mg alloys can be considered as promising alternatives to aluminum and steel alloys that are widely used [4]. Automotive industries in North America and Europe have used magnesium alloys for the fabrication of various parts, such as the steering wheel frame, seat frame, cylinder head, and body of the oil pump [2, 5]. These parts are usually produced via a casting process because of the ability to form complicated cast shapes with high productivity. In particular, the Mg-9Al-1Zn alloy (AZ91) is widely used for different engineering applications. However, the viability of Mg alloys
* Mitsuhiro Okayasu [email protected] 1
Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushimanaka, Kita-ku, Okayama 700-8530, Japan
as replacements for cast aluminum alloys and cast iron for the manufacture of safety-critical automobiles parts is significantly restricted; this is because of the poor mechanical properties that arise from the presence of various defects, such as cracks, blow holes, inclusions, and shrinkage porosities [6]. Hence, the
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