Precipitation and work hardening in high strength AlZnMg(Cu,Zr) alloys

Precipitation and work hardening processes taking place in high strength AlZnMg alloys (7xxx series) were investigated by compression tests, differential scanning calorimetry and transmission electron microscopy. The results show that addition of Cu changes strongly the temperature of GP zone-->intermediate phase transition. In the range of the zone formation the strength of the material increases strongly by the addition of Cu and it depends on the ageing temperature. At the same time the work hardening remains unchanged in this temperature range and is hardly effected by the addition of Cu. The addition of Zr leads to an extremely fine-grained structure and in the AlZnMgCuZr alloy a ''duplex'' GP-zone structure is formed, causing a ''duplex'' behaviour of this alloy.