Effect of substrate material and roughness on the properties of magnesium AZ31-B alloy cast on horizontal single belt casting simulator.

摘要

Strips of magnesium alloy AZ31-B were cast on a single belt casting simulator with moving-mold system. A mixture of carbon dioxide (CO 2) and sulfur hexafluoride (SF6) gases was used as a protective gas during melting and casting of the magnesium alloy. The castability of the magnesium alloy strips was investigated for different types of substrates: smooth low carbon steel substrate, copper with six different roughnesses, graphite-coated smooth steel and graphite-coated copper with different roughnesses. Moreover, the effect of strip thickness on the casting properties were investigated. The heat flux through the copper substrate was higher than that through the steel substrate, while coated substrates showed lower heat fluxes than the uncoated substrates. The highest heat flux was recorded for the grooved (rough) substrate with 0.15 mm depth, while further increasing the surface roughness (depth) resulted in a decrease in the heat flux. Decreasing the heat flux reduced the quality of the top surface of the strips. However, as the thickness of the strip decreased, although the heat flux decreased, the quality of the top surface increased. As the heat flux increased, the grain sizes of the strips were reduced while the secondary arm spacing (SDAS) decreased. The mechanical properties, TS, YS and HV increased when the heat flux increased. Although magnesium oxide normally appears in white, the black color of the outer MgO layer of the strips formed under unprotected conditions is due to the presence of sub-micron MgO particles.