Modifying AM60B magnesium alloy die cast surfaces by friction stir processing

This experiment was done to evaluate the feasibility of locally modifying the surface properties of magnesium alloy die castings with friction stir processing. The Mg alloy used for the study was AM60B, nominally Mg-6Al-0.13Mn, wt%. Friction stir passes were made with a translation speed of 1.7 mm/s using tool rotation speeds of either 1250 or 2500 rpm. Stir passes with good appearance were obtained with both conditions. In some cases up to 5 passes were overlapped on a single bar to produce stir zones with cross sectional dimensions of about 1.5 × 10 mm. Metallographic examination indicated that the stir zones were largely comprised of equiaxed grains on the order of 5-10 μm in size. Hardness mapping showed that the stir zones experienced increases of about 21% compared to the as-cast metal. Room temperature testing showed that, compared to the cast metal, the stir zones had about flow stresses nearly 20% higher with about twice the tensile elongation.