Investigation of the age hardening behaviour of 6063 aluminium alloys refined with Ti, RE and B

The purpose of this study is to obtain a better understanding on the effect of ageing on the hardness of 6063 aluminium alloys refined with Ti, cerium-rich mixtures of rare earth (RE) and B with the aids of SEM, EDS, TEM, DSC, etc. The following conclusions have been obtained: the 6063 alloy with the joint additions of Ti, B and RE (10 w(Ti)/w(B) mass ratio) has the finest grain, compared to alloys with Ti or Ti and RE additions. Artificial ageing must be performed more than 7 d after extrusion. The 6063 alloys refined with Ti, Ti + RE or Ti + RE + B all have better ageing behaviour. It takes shorter ageing time to obtain a hardness near peak ageing hardness and there is no obvious decrease of ageing hardness of the alloys until ageing for 6 h at 200 °C. The addition of RE forms Al–Si–Mg–RE intermetallic constituents, resulting in lower strength of alloys than that with Ti addition.