Effects Of The Solidification Condition And Cu Concentration On The Microstructure And Mechanical Properties Of A357Alloy Barrel-shape Castings

This paper employs the low pressure casting method to prepare A357alloybarrel-shape sample. effects of the solidification condition and copper concentrationon the microstructure and mechanical properties of the barrel-shape castings havebeen investigated.The effects of different wall thickness on the microstructure and mechanicalproperties have been investigated. For the as-cast samples, the thicker the wall, thelarger the secondary arm spacing, the more heterogeneous distribution of eutectic Si,the larger the longitudinal/cross-sectional ratio. The thicker the wall, the less themodification effect. In barrel-shape castings as the secondary arm spacing is criticalfor the tensile strength, and the roundness of the eutectic Si is critical for the ductileproperty, therefore the castings with large wall-thickness have a major decrease in thetensile strength, specifically for the elongation rate. The tensile strength of the as-castsample prepared by sand casting with20mm wall-thickness is143MPa, while the10mm wall-thickness sample is173MPa, and the elongation increases from3%-7%.After T6heat treatment, the thicker the casting sample, the less the spheroidization ofeutectic Si. The tensile strength of the as-cast sample prepared by sand casting with20mm wall-thickness after T6heat treatment is233MPa, while the10mm sample is283MPa. Increases about25%.The effects of chill on the microstructure and mechanical properties of A357barrel-shape alloy has been investigated. The increase of solidification cooling rate isachieved by adding chiller blocks. Under the same conditions, the elongation issignificantly increased after adding chiller blocks. The tensile strength of the as-castsample prepared by sand casting with20mm wall-thickness and chiller block is176MPa, while the20mm wall-thick sample is147MPa, and the elongation decreasesfrom9%to4%. After T6heat treatment, the tensile strength of the as-cast sampleprepared by sand casting with20mm wall-thickness with chiller block is316MPa,while the20mm wall-thick sample is259MPa, the elongation decreases from8.9%to3.8%. The heat treatment can significantly increases the mechanical properties ofA357barrel-shape samples.In the barrel-shape sample prepared by low-pressure casting, the mechanicalproperties are regional related. In both casting samples with large and small coolingrate, the mechanical properties near the sprue are higher than those not nearby.Minor copper addition will affect the mechanical property of A357alloy. For theas-cast sample, the presence of minor copper can slightly enhances the tensile strengthand elongation rate, and have a larger effect on the elongation. The mechanicalproperties of the barrel-shape casting can be significantly improved after T6heat treatment.