Effects of β-precipitates on the low temperature toughness of Al-5%Mg and equi-axed 5083 alloys

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  • Al‐5%Mgおよび5083等軸粒合金のじん性に及ぼすβ相の影響
  • Al 5パーセント Mg オヨビ 5083トウジクリュウ ゴウキン ノ ジンセ

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Low temperature toughness of Al-Mg alloys with equi-axed grains has been investigated by means of the tear test at RT to -196°C and effects of β-precipitates on modes of fracture were discussed. The unit propagation energy (UPE) and the tear strength at -196°C decreased markedly on aging above 150°C. This was successfully attributed to the intergranular fracture as a result of precipitation of fi phase on grain boundaries. UPE was expressed as a function of the fraction of the grain boundary fracture fGB, as<br>UPE=-4.6fGB + 4.2, kg-mm/mm2.<br>It has been shown that dimple patterns are formed on the grain boundary surface after sufficient aging. The dimples were formed on β-precipitates larger than 0.1μ. When β-precipitates were smaller than 0.1μ no dimple was found on grain boundaries.<br>Based upon the observations, it was concluded that when β-precipitates were small (<0.1μ), ductile transgranular fracture was the main mode of fracture and when β-precipitates were large (>0.1μ), grain boundary fracture controlled the toughness of Al-Mg alloys at low temperature.

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