Hard Spots in ADC12 Die Casting Cylinder Block Used for Air Compressor

The hard spots are investigated in ADC12 die casting cylinder blocks for air compressors using metallographic method and a micro- hardness tester. The results show that the hard spots have two main shapes. There is a nonuniform micro-hardness distribution within a hard spot. Energy dispersive spectrometry (EDS) analysis reveals that these hard spots are some kind of mixture of oxide and carbide, which are formed during melting and die casting process.