EFFECT OF Cd ADDITION ON THE AGING PROCESS OF Al--Si--Cu--Mg CAST ALLOY
Cd对铸造Al-Si-Cu-Mg合金时效过程的影响

The addition of Cd promotes the age-hardening process of Al-Si-Cu-Mg alloy, increases the peak hardness and reduces the time to reach peak hardness. The UTS increases 20% when 0.27% Cd is added in, on the contrary, strength decreases if the content of Cd exceeds 0.27%. The re sults of SEM, DSC and TEM reveal that trace addition Cd stimulates nucleation of metastable phases and accelerates the following aging process of alloys. At the same time, some larger Cd-rich particles and stable phases formed in the matrix, which strengthen alloys as second-phase. In the combined action of those two kinds of precipitates, the peak strength of alloy improves remarkably. However, when the content of Cd exceeds 0.27% some Cd-rich phases and pure Cd particles form, and those particles soften grain boundary and result in the decrease of alloy strength.