EFFECT OF MODIFICATION ON ALUMINUM-MATRIX OF AL-SI-MG ALLOYS

The influence on the aluminium matrix of chemical modification by addi tion of strontium or sodium has been investigated in 356 aluminium all oy cast in a permanent mould. Solution heat treatment time and artific ial aging time were the two variables examined for the heat treatment study. In the as cast condition, modification does not have an influen ce on the overall hardness (i.e. that of the aluminium matrix and eute ctic silicon) or on the microhardness of the aluminium matrix. Modific ation does however have an effect on the aluminium matrix of the heat treated alloy. The hardness and yield strength of the modified alloys are lower after the T6 temper compared with the unmodified alloy. Hard ness-yield strength relationships have been established.