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Effect of thermomechanical treatment on properties and structure precipitates in high strength aluminium alloys.

Dutkiewicz J., Morgiel J., Lityńska L.

Inżynieria Materiałowa

1998

R. XIX, nr 3

423-428

The effect of thermomechanical treatment on the structure and mechanical properties of 7278A (1) and AlCuAgMg alloys (2,3) containing 6%Cu, 0.4-0.8%Ag and 0.4-0.8%Mg in wt% was investigated. The alloys were continuously cast, then extruded, cold rolled and aged at temperatures up to 165 degrees centigrade. Alloy 1 attained maximum hardness of 210 HV and UTS 700 MPa after ageing at 120 degrees centigrade for 24 h. The 75% rolling prior to ageing resulted in 230 HV. A day ageing at 120 degrees centigrade caused precipitation of the eta' phase. The rolled and aged alloys contained the equilibrium eta phase formed by nonhomogeneous nucleation what causes smaller strengthening effect. Alloy 2 attained maximum hardness of 150 HV after ageing at 165 degrees centigrade for 24 h, i.e. significantly lower than the 7278A alloy. The deformation by rolling in the as quenched state increased UTS up to about 400 MPa after 75% rolling i.e. 200 MPa less than in the case of the 7278 alloy. Alloy 3 of higher Ag and Mg content reached maximum hardness of 190 HV during ageing, and 230 HV after deformation and ageing i.e. close to the 7000 alloys. TEM studies allowed to identify the main hardening phases as Theta' and Omega, the latter resulting from presence of Ag and forming platelets lying on {111} matrix planes. The deformation promoted the Theta' phase formation.