Alloying and alloy composition of 7 series high-strength aluminium alloys

Alloying and alloy composition of 7 series high-strength aluminium alloys

The main alloying elements of 7 series high strength aluminium alloys are Zn, Mg, Cu, Zr and impurity elements Fe and Si. m(Zn)% is 7-12% and m(Mg)% is 2-3%. m(Mg)% is the main strengthening phase of Zn and Mg, MgZn2. increasing the Zn and Mg content increases the strength of the alloy, but decreases the toughness and SCC. m(Cu)% is about 2-3%.

m(Cu)% is approximately 2-3%. m(Cu)% increases the strength, plasticity and SCC of the alloy due to the Cu atoms entering the GP zone and retarding ageing precipitation. m(Cu)% decreases the potential difference between grain boundaries and intra-crystalline, increasing SCC.

The m(Zr)% is approximately 0.05%-0.15%. m(Zr)% also increases the strength, toughness and SCC of the alloy because Al3Zr has two structures: a tetragonal structure that precipitates from the melt and refines the grain, and a spherical structure that precipitates in homogenisation and co-lays with the matrix, inhibiting recrystallisation during heat treatment.

The m% of Fe and Si should be less than 0.1%. They are harmful elements that reduce the fracture toughness of the alloy. The reason is the formation of AlFeSi brittle phase, in the plastic deformation of the matrix and brittle phase deformation is not coordinated and the formation of small cracks.