Al–Si–Mg based cast alloys have been used widely for thixoforming processes. Amongst them A356 and A357 are the most common alloys used to obtain near-net shape products because of good casting characteristics, weldability and corrosion resistance [8]. Amongst the thixoforming processes available, forging has considerable potential for severe plastic deformation and improvement in mechanical properties [9]. The investigations by Tahamtan et al. [10] and [11] showed significant improvement in tensile properties of thixoforged A356 alloy compared to that of rheocast and gravity-cast samples. Recently, in-situ reinforced aluminum based metal matrix composites (AMMCs) are emerging as one of the most promising alternatives for eliminating the inherent defects associated with ex-situ reinforced AMMCs. It has been reported that Al based composites reinforced with TiB2 particles have clean interfaces, and moreover TiB2 particles refine the size of eutectic Si by restricting its growth and thereby enhancing the mechanical properties significantly [12], [13] and [14]. In addition, metal forming in the mushy state zone has gained importance for manufacturing of AMMCs [15].
The solution treatment followed by ageing plays a key role in improving the mechanical properties and durability of metallic components [16]. The strengthening mechanisms in the Al–Si–Mg alloy system has been attributed to the precipitation of phases from a supersaturated solid solution (SSS) elucidated by different techniques such as XRD and TEM reported elsewhere [17]. The precipitation sequence and reactions in Al–Si–Mg alloy can be described by Eq. (1) as follows:
Al–Si–Mg based cast alloys have been used widely for thixoforming processes. Amongst them A356 and A357 are the most common alloys used to obtain near-net shape products because of good casting characteristics, weldability and corrosion resistance [8]. Amongst the thixoforming processes available, forging has considerable potential for severe plastic deformation and improvement in mechanical properties [9]. The investigations by Tahamtan et al. [10] and [11] showed significant improvement in tensile properties of thixoforged A356 alloy compared to that of rheocast and gravity-cast samples. Recently, in-situ reinforced aluminum based metal matrix composites (AMMCs) are emerging as one of the most promising alternatives for eliminating the inherent defects associated with ex-situ reinforced AMMCs. It has been reported that Al based composites reinforced with TiB2 particles have clean interfaces, and moreover TiB2 particles refine the size of eutectic Si by restricting its growth and thereby enhancing the mechanical properties significantly [12], [13] and [14]. In addition, metal forming in the mushy state zone has gained importance for manufacturing of AMMCs [15].รักษาโซลูชันตามริ้วรอยมีบทบาทสำคัญในการปรับปรุงคุณสมบัติทางกลและความทนทานของชิ้นส่วนโลหะ [16] มีการบันทึกกลไกที่เข้มแข็งในระบบโลหะผสม Al – Si – มิลลิกรัมฝนระยะจากโซลูชันทึบ supersaturated (SSS) elucidated โดยเทคนิคต่าง ๆ เช่น XRD และยการรายงานอื่น ๆ [17] ฝนลำดับและปฏิกิริยาในโลหะผสม Al – Si – มิลลิกรัมสามารถอธิบาย โดย Eq. (1) ดังนี้:
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