The effect of average cooling rates on the microstructure of the Al–20% Si high pressure die casting alloy used for monolithic cylinder blocks
The effect of average cooling rates on the microstructure of the Al–20% Si high pressure die casting alloy used for monolithic cylinder blocks
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DOI：
10.1016/j.jmatprotec.2007.10.023
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发表时间：
2008-07
影响因子：
6.3
通讯作者：
H. Yamagata;W. Kasprzak;M. Aniolek;H. Kurita;J. Sokolowski
中科院分区：
文献类型：
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作者：
H. Yamagata;W. Kasprzak;M. Aniolek;H. Kurita;J. Sokolowski
利用新型通用冶金模拟分析平台研究了平均冷却速率对过共晶Al-20% Si合金显微组织的影响。对实验室试样进行了初晶Si尺寸和非平衡α-Al的二次枝晶臂间距随冷却速度的定量测量。为了分析高压铸造缸体的微观组织，了解其复杂的凝固过程，开展了此项研究。随着冷却速率从4.9 °C/s增加到82.9°C/s，初晶Si的等效直径从89.7±17.3 μm减小到16.5±3.8 μ m，二次枝晶间距从22.1±5.9 μ m减小到5.1±0.8μm。气缸体显微组织的观察表明，初晶硅的大小几乎是相同的，在次表面和中心位置的孔壁。非平衡α-Al相的二次枝晶臂间距和共晶Si尺寸在孔壁亚表面处明显减小。基于UMSA实验室测量，确定发动机孔壁中的初生Si（在表面下和中心处）以约72-74°C/s的冷却速率从液体熔体成核为第一相。结果表明，发动机孔壁次表面的非平衡α-Al枝晶在约85°C/s的冷却速率下从半固态熔体中形核，而孔壁中心的非平衡α-Al枝晶在约49°C/s的冷却速率下形核。研究表明，在注射过程开始前，部分初晶Si颗粒在注射室中形核，而α-Al枝晶和共晶Si在型腔中形核。因此，证明了注入的过共晶Al-20% Si液态熔体具有固态初生Si颗粒。
The effect of average cooling rates on the microstructure of the hypereutectic Al–20% Si alloy was investigated using the novel Universal Metallurgical Simulator and Analyzer Platform. The quantitative measurements of the primary Si size and the Secondary Dendrite Arm Spacing of the non-equilibrium α-aluminum as a function of the cooling rates was performed for the laboratory test samples. This research was carried out in order to analyze the microstructure of the high pressure die cast cylinder block and to understand its complex solidification process. The Equivalent Diameter of the primary Si decreased from 89.7±17.3 to 16.5±3.8μm and the Secondary Dendrite Arm Spacing from 22.1±5.9 to 5.1±0.8μm with an increase in the cooling rate from 4.9 to 82.9°C/s. Observations of the cylinder block microstructures revealed that the primary Si size was nearly identical at the subsurface and the centre locations of the bore wall. The Secondary Dendrite Arm Spacing of the non-equilibrium α-aluminum phase as well as the eutectic Si size was significantly smaller at the subsurface of the bore wall. Based on the UMSA laboratory measurements it was determined that the primary Si in the engine bore wall (both at the subsurface and the centre) nucleated as a first phase from the liquid melt at a cooling rate of approximately 72–74°C/s. It was found that the non-equilibrium α-aluminum dendrites at the engine bore wall subsurface nucleated from the semi-solid melt at a cooling rate of approximately 85°C/s, while at the centre of the bore wall at approximately 49°C/s. Research revealed that some primary Si particles nucleated from the beginning of the melt pouring into the shot sleeve prior to the injection process while the α-aluminum dendrites and eutectic Si nucleated in the die cavity. Therefore, it was proven that the injected hypereutectic Al–20% Si liquid melt had solid primary Si particles.