Positron Annihilation Studies of the Subsurface Zone in Aluminium Alloys

The paper presents positron lifetime studies of the subsurface region of the aluminium cast AK64 alloy containing silicon as a main alloying element after sliding against stainless steel in the pin-on-disc tester. The subsurface zone of the depth exceeding 150μm has been detected. The scanning electron microscopy revealed only the plastically deformed region occurring at the depth up to ca. 50μm and cracks at the depth less than 30μm. The comparison with the results obtained for the AK12 alloy containing almost a twice higher amount of silicon demonstrates the influence of the hard silicon rich particles on the total depth of the subsurface zone. A higher amount of hard particle prevents to some extend the propagation of defects inside the material.