STUDY OF MICROSTRUCTURE AND MECHANICAL PROPERTIES OF CONTINUOUSLY CAST AA6111 STRIPS FOLLOWING CASTING, ROLLING AND HEAT TREATMENTS

摘要

Strips of AA6111 automotive alloy were strip cast on a horizontal single belt strip caster (HSBC) and on an equivalent casting simulator, both located at McGill's Metal Processing Centre. The effects of belt materials (copper and steel), strip thickness, belt speeds and casting temperatures, on the strip's as-cast microstructures were presented. In this paper, we report on the hot-rolling, cold-rolling, and heat treatment of cast sheet samples down to thicknesses and microstructures appropriate for automotive body panels. Different scenarios regarding rolling and heat treatments were considered in order to evaluate the possibility of simplifying the conventional processing of AA6111 strip products using this novel HSBC technology. A T4 treatment consisting of solution heat treatment, quenching, and natural aging, was selected to adjust the material's mechanical properties. This was followed by a paint-baking step to simulate the conventional process for automotive sheet. The evolution of strip microstructures during rolling and heat treatment processes were investigated using both optical and Scanning Electron Microscopy (SEM). Similarly, tensile tests and microhardness measurements were made on the sample strips in order to evaluate the effects of rolling and heat treatment on the mechanical properties of these strip cast products.