Age-Hardening Behavior of Al-Si-Cu Base Cast Alloys

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  • Al-Si-Cu系鋳造合金の時効硬化挙動
  • Al-Si-Cuケイ チュウゾウ ゴウキン ノ ジコウ コウカ キョドウ

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Abstract

  Age-hardening processes were investigated on pure Al-Si-Cu and Al-Si-Cu-Mg alloys containing about 7mass%Si, 2.72 to 4.08mass% Cu and 0 to 0.47mass%Mg and also on a commercial JIS-AC4B alloy by using a TEM, Vickers macro hardness tester and EPMA. A series of alloy specimens were solution treated at 773K for 10h, and subsequently aged at 433K and 473K for 10min to 104min. The typical hardness-aging time relations are obtained for each alloy specimen. Age-hardnening occurs faster in the Al-Si-Cu-Mg and AC4B alloys than in the ternary Al-Si-Cu alloy. The maximum hardness of the specimen aged at 433K increases from HV95 to HV152 as the Mg content of the alloy increases from 0 to 0.43mass%. TEM shows the high density dislocations distributing around the eutectic Si particles which are expected to have formed in the α phase during quenching from the solution-treatement temperature, because of the difference in the coefficient of thermal expansion between the α matrix and eutectic Si. The formation of the GP Zone is suppressed and the precipitation of θ’ is promoted in the ternary Al-Si-Cu alloy which contains higher density dislocations. A number of tiny particles of the Mn-rich compound precipitate in the α matrix of the solution-treated AC4B alloy, which decreases the Cu content of the α phase and the age-hardening ability of the AC4B alloy.

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