No.10（2015）3.Effects of porosity on impact properties of AD12 alloy castings

Shinji Nishimura, Kenji Sato

  The effects of porosity volume, size and distribution in JIS AD12 aluminum alloy castings on impact properties were investigated. Three different porosity volumes were prepared by controlling gas content of the melt. Volume fraction, sizes and distribution were evaluated by density, cross-sectional observation of microstructure using an optical microscope and radiographic examination. The toughness was evaluated using an instrumented Charpy impact tester. The impact fracture surfaces observed using an SEM were grouped into two categories, the fracture surfaces with gas porosity and those without. The impact values of specimen group without gas porosity proportionally increased with the logarithm of the solidification rate. The porosity reduced the crack initiation energy, while giving only limited effect on the crack propagation energy. The impact value excluding the influence of solidification rate proportionally decreased with increased volume fraction of porosities. The tendency of impact values excluding the influence of solidification rate was influenced by the size and the distribution of porosities. The crack propagation showed less steep gradient with the increased volume fraction of porosity.

Keywords
Aluminum, Toughness, Charpy impact test, Porosity

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