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Effect of the Vacuum Heat Treatment on the Microstructure and Mechanical Properties of the Galvanized‑Q235/AZ91D Bimetal Material Produced by Solid–Liquid Compound Casting Jun Cheng2 · Jian‑hua Zhao1,2   · Dengzhi Zheng2 · Ke He2 · Yu Guo2 Received: 4 August 2019 / Accepted: 13 October 2019 © The Korean Institute of Metals and Materials 2019

Abstract The galvanized-Q235/AZ91D bimetallic material was achieved via solid–liquid compound casting, and the effect of the heat treatment at 250 °C for 3 h on the microstructure and mechanical properties of the galvanized-Q235/AZ91D bimetallic material were investigated. The interface zone in the galvanized-Q235/AZ91D was composed of three different layers which were the ­FeAl3 + α-Mg, (α-Mg + MgZn), and α-Mg + (α-Mg + MgZn) from the galvanized-Q235 to AZ91D, successively. After the heat treatment, the (α-Mg + MgZn) eutectic structure was transformed into ­Al5Mg11Zn4 to promote the microhardness from 139.2 HV to reach 298.8 HV. In addition, the α-Mg and (α-Mg + Mg12Al17) eutectic structure in AZ91D were separately transformed into (α-Mg + Al5Mg11Zn4) and A ­ l5Mg11Zn4 resulting in the increasement of microhardness, from 59.5 to 173.4 HV and 294.2 HV, respectively. Moreover, the interfacial shear strength was changed from 11.23 to 24.63 MPa due to the formation of ­Al5Mg11Zn4 and the vanishment of MgZn. Keywords  Solid–liquid compound casting · Heat treatment · Microstructure · Interface zone · Hot-dip galvanizing · Shear strength · Microhardness

1 Introduction Nowadays, magnesium alloys were employed in the automotive and aerospace fields for economic savings and ecological protection due to the lightest materials than most of construction material and many advantages such as good machinability and cast ability as well as high damping capacity [1, 2]. However, their high temperature corrosion and wear resistance were poor which limited its further application [3, 4]. By contrast, galvanized steel had the better corrosion and wear resistance [5]. Therefore, the combination of steel and magnesium alloy could satisfy the requirements of the integral performance as well as the light weight for some industrial applications. Instead, the combination of steel and magnesium alloy was very difficult due to the huge * Jian‑hua Zhao [email protected] 1



State Key Laboratory of Mechanical Transmission, Chongqing University, Chongqing 400044, China



College of Materials Science and Engineering, Chongqing University, Chongqing 400045, China

2

differences in physical and chemical properties such as the melting point and solid solubility [6]. Among these differences, the fact that there is no existence of Fe–Mg intermediate compound is the biggest challenge for the joining of steel and magnesium alloy. According to previous researches [7, 8], the interlayer is beneficial to realize metallurgical bond of steel and magnesium alloy. Currently, the joining of steel and magnesium alloy has been achieved by many methods such as ERW (electric resistance welding) [7, 9], FSW (fricition stir