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

The galvanized-Q235/AZ91D bimetallic material was achieved via solid-liquid compound casting, and the effect of the heat treatment at 250 degrees 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 + alpha-Mg, (alpha-Mg + MgZn), and alpha-Mg + (alpha-Mg + MgZn) from the galvanized-Q235 to AZ91D, successively. After the heat treatment, the (alpha-Mg + MgZn) eutectic structure was transformed into Al5Mg11Zn4 to promote the microhardness from 139.2 HV to reach 298.8 HV. In addition, the alpha-Mg and (alpha-Mg + Mg12Al17) eutectic structure in AZ91D were separately transformed into (alpha-Mg + Al5Mg11Zn4) and Al5Mg11Zn4 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.