Tensile Properties of the Subsurface and Center Regions of AA6111 Direct-Chill-Cast Ingot in Semisolid State and Their Hot Tearing Susceptibility

Abstract

AA6111 alloys are widely used in the automotive industry owing to their high strength/weight ratio, good corrosion resistance, and reasonable formability. During their manufacture through ingot metallurgy via direct chill (DC) casting, the alloys often suffer from hot tearing, limiting DC casting productivity. The present study focused on evaluating the mechanical properties in the semisolid state and the hot tearing susceptibility of AA6111 DC-cast ingot in the subsurface and center regions. The mechanical behavior of two different regions at high temperatures above solidus was studied using smoothed and notched samples. Tensile tests were performed using the Gleeble 3800 thermomechanical testing unit, and the digital image correlation method was applied to measure the strain evolution. The change in the grain structure in the subsurface and the presence of a high-volume fraction of needle-like β-Fe intermetallics significantly reduced the ductility of the cast ingot in the subsurface region. The hot tearing susceptibility in the subsurface region of the cast ingot was higher than that in the center region. The notch effect is more significant in the subsurface on the stress sensitivity in the presence of stress raisers compared with that in the center region.

Keywords

• AA6111 DC-cast alloy
• high-temperature tensile properties
• hot tearing susceptibility
• brittle temperature range