Structure of GP zones in Al-Si matrix composites solidified under high pressure

The structure of the Guinier-Preston (GP) zones precipitated in the Al-Si matrix composites after natural aging is investigated. The results show that, after natural aging, spherical GP zones with a diamond crystal structure form in the supersaturated α-Al matrix produced by high pressure solidification. The lattice parameter of the GP zones is 1.62 nm and their structure consists of Si3 atomic clusters. The GP zones disappear and Si crystals are formed in the α-Al matrix after heating to 673 K. The precipitation sequences in the supersaturated α-Al matrix can be summarized as: α-Al (SSSS)→GP zones→equilibrium Si phase.