Showing papers by "Amol A. Gokhale published in 2004"

Microstructure and age hardening response of cast Al-Mg-Sc-Zr alloys

Abstract: Al-Mg-Sc-Zr alloys have been investigated in recent years [1–3]. Sc and Zr additions to Al-5%Mg alloy were shown to refine the as-cast grain structure, increase strength of rolled sheets and reduce sub-grain size [4]. A series of alloys containing 0.30–0.35%Sc, 0.10– 0.16%Zr and 1.1–6.3%Mg were produced in rolled sheet form and shown to possess higher tensile properties compared to conventional Al-Mg based alloys [3]. In addition, the grain size of Zr containing alloy was found to be more stable at high temperatures than that of Zr-free Al-3%Mg-0.2%Sc alloy under superplastic deformation conditions [5]. The effect of Mg content in the Al-Mg-Sc-Zr alloy system on as-cast grain structure and hardening on direct aging has not been studied systematically. Such a study is considered important, since it can lead to the development of alloys with improved castability and weldability combined with high strength compared to conventional casting alloys. Also hardening on direct ageing of the as-manufactured components may be an added advantage in situations where a separate solution treatment may not be possible or may be undesirable due to problems associated with residual stresses and distortion. Chemical compositions of various alloys investigated are given in Table I. The alloys are designated by the nominal Mg content, and will be referred as such. The starting materials used in making the alloys were: 99.85% pure Al, Mg-30%Zr and Al-2%Sc ingots. The alloys were melted in an air induction melting furnace under flux cover, superheated to 760 ◦C, cooled to 700 ◦C and cast in dried M.S. molds as 25 mm diameter × 200 mm long ingots. Samples for metallography and age hardening studies were extracted leaving 25 mm height from the bottom of the ingots. Standard metallographic procedures were used. Samples were aged without prior homogenization or solution treatment in muffle type furnaces with job temperature variations within ±2 ◦C. Vickers hardness using 5 kg load was measured on the cross section of the ingots. Foils were