Abstract
The contraction and strength in liquid-solid coexisting zone of Al-Zn-Mg alloys were investigated. The liquid-solid zone may be divided into two stages by the strength boundary. One stage of higher temperature was called strength minimum zone and another of low temperature was strength increase zone. In Al-5%Zn-Mg alloys, the strength increase zone was increased considerably at less than 2%Mg, and the strength minimum zone was increased at more than 2%Mg. The strength minimum zone was increased and the strength increase zone was decreased by the individual addition of Ti, 0.5%Zr and 0.2%Be to Al-5%Zn-2%Mg alloy. The reverse tendencies were recognized by addition of Mn, Cu and Cr. The strength increasing rate of Al-Zn and Al-5%Zn-Mg alloys decreased with the increase of Zn and Mg content, that of Al-5%Zn-2%Mg alloy increased by the addition of Ti, 0.5%Zr and 0.2%Be. Al-Zn alloys with low Zn and Al-5%Zn-Mg alloys with high Mg decreased the linear contraction rate and the elongation. Those of Al-5%Zn-2%Mg alloy decreased by addition of Ti, 0.5%Zr and 0.2%Be and increased by addition of Mn, Cu and Cr.
