A Study on Microstructure and Properties of an A356-20%SiC Composite after Equal Channel Angular Extrusion
實驗結果顯示，轉角120°無外弧角Ψ之模具擠型之試片破斷情形較不嚴重。不同擠型速率及擠型溫度低於100℃均會使經過轉角120°有外弧角Ψ模具之試片產生階梯狀破斷，而200℃、300℃擠型後則無。25℃至75℃之試片擠型後常溫硬度值與原材硬度值HV 88相近，300℃擠型試片之常溫硬度值則降至HV 84。試片內部SiC堆積於試片表面及轉角內側區域，但200℃及300℃試片SiC分布較均勻。試片內部孔隙率，由擠型溫度25℃之7.5%下降至擠型溫度300℃之4%。觀察不同平面之孔隙率可知擠型後試片無明顯之優選方向。|
In this research, an A356-20%SiC composite through different equal channel angular extrusion (ECAE) conditions of mold type、extrusion speed and extrusion temperature were investigated. Microstructure and properties of the A356-20%SiC composite through different extrusion temperatures were studied. The A356-20%SiC composite through 120°channel angle without additional angle Ψ extrusion had less breakage. The A356-20%SiC composite through 120°channel angle with additional angle Ψ extrusion generated ladder shape breakage with changing extrusion speed and extrusion temperatures under 100℃. However, the A356-20%SiC composite of 200℃ and 300℃ extrusion did not generated ladder shape breakage. Hardness of specimens through 25℃ to 75℃ extrusion resembled to hardness of the raw material which was HV 88. When extrusion temperature increased to 300℃, hardness was decreased to HV 84. SiC particles were accumulated at specimen surface and region of inner point of intersection of the two channels； however, that of 200℃ and 300℃ extrusion specimen was distributed more uniformly. The porosity fraction at 25℃ extrusion temperature is 7.5%, which was decreased to 4% at 300℃ extrusion temperature. No prefer orientation was produced by observing porosity fraction of different planes.
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