Effect of heat treatment and Fe content on the microstructure and mechanical properties of die cast Al–Si–Cu alloys

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• Solution and ageing significantly improve the tensile strength of die-cast Al–Si–Cu alloy.

• Low Fe is necessary for improving the ductility in the solution and aged alloy.

• Cu-rich phase is dissolved during solutionising of die-cast Al–Si–Cu alloy.

• θ′ and Q′ precipitates co-exist in die-cast Al–Si–Cu alloy for strengthening.

• Solution and ageing do not alter the size and morphology of αAlFeMnSi phase.


The effect of solution and ageing heat treatment on the microstructure and mechanical properties of the die-cast Al–9 wt.%Si–3.5 wt.%Cu alloys containing 0.1–1.0 wt.% Fe was investigated. The results showed that the dendritic primary α-Al phase was varied from 20 to 100 μm in size and the globular α-Al grains were smaller than 10 μm in size. The Fe-rich intermetallics exhibited coarse compact or star-like shapes with the sizes from 10 to 20 μm and the fine compact particles at an average size of 0.75 μm. The solution treatment of the alloys could be achieved in a short period of time, typically 30 min at 510 °C, which dissolved the Cu-rich intermetallics into the primary α-Al phase and spheroidised the eutectic Si phase. During the subsequent ageing treatment, numerous fine precipitates of θ′ and Q′ phases were formed to provide effective strengthening to the α-Al phase, significantly improving the mechanical properties. Therefore, Fe content in the die-cast Al–Si–Cu alloys needs to be controlled at a low level in order to obtain the improved ductility and strength under solution and aged condition.

0.1~1.0wt.% Fe를 함유한 다이캐스트 Al-9wt.%Si-3.5wt.%Cu 합금의 미세 구조 및 기계적 특성에 대한 용체화 및 시효 열처리의 영향을 조사했습니다. 그 결과 수지상 1차 α-Al 상은 크기가 20~100μm로 다양하고 구형 α-Al 입자의 크기는 10μm 미만인 것으로 나타났습니다. Fe가 풍부한 금속간 화합물은 크기가 10~20μm인 조대 조밀하거나 별과 같은 모양과 평균 크기 0.75μm의 미세 조밀 입자를 나타냈습니다. 합금의 용체화 처리는 일반적으로 510°C에서 30분의 짧은 시간 내에 달성될 수 있으며, 이는 Cu가 풍부한 금속간 화합물을 기본 α-Al 상으로 용해하고 공융 Si 상을 구형화합니다. 후속 시효 처리 동안 θ' 및 Q' 상의 수많은 미세 석출물이 형성되어 α-Al 상에 효과적인 강화를 제공하여 기계적 특성을 크게 향상시켰다. 따라서 다이캐스트 Al-Si-Cu 합금의 Fe 함량은 용체화 및 시효 조건에서 향상된 연성 및 강도를 얻기 위해 낮은 수준으로 제어되어야 합니다.

Graphical abstract

Effect of heat treatment and Fe content on the microstructure and mechanical properties of die-cast Al–Si–Cu alloys
Effect of heat treatment and Fe content on the microstructure and mechanical properties of die-cast Al–Si–Cu alloys





Mechanical properties




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