Hot tearing of machinability improved 2xxx aluminum alloy of high tin content with manganese and chromium addition

Abstract

In this study, the effect of Mn and Cr addition on high temperature mechanical properties of a machinable 2xxx alloy with high Sn content was systematically investigated. Tensile test during solidification was carried out, using an electromagnetic induction heating tensile test machine. Stress-strain curve, tensile strength, fracture strain (elongation), Zero Strength Temperature (ZST) and Zero Ductility Temperature (ZDT) were evaluated. To determine the solidification range of the 2xxx alloy with high Sn content, the specific heat were continuously measured in the range from room temperature to 700°C using an insulating type measuring device of specific heat. It was found that the tensile strength during solidification steeply increased with Mn and Cr addition, and the temperature range between ZST and ZDT became wider, in comparison with those without Mn and Cr addition. It was presumed that the crack susceptibility of the alloy increased by Mn and Cr addition. Fractography on the high temperature clearly distinguished the fracture property and fracture behavior of the alloys with and without Mn and Cr addition. Formation of intermetallic compounds at later stage of solidification was different from with and without Mn and/or Cr addition. Furthermore, by comparing the tensile strength with the casting practice, the effect of Mn and Cr addition on the crack susceptibility of direct-chill cast billets was severely attributed to crystallization of these compounds. © 2008 The Japan Institute of Metals.