Mechanical properties of laser welded semi-solid metal cast A356 alloy

Master Thesis


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University of Cape Town

The high usage of Al and its alloys in both the automotive and aerospace industries is attributed to its excellent specific strength and corrosion resistance. High demand of Al usage has led to the improvement of both the casting techniques and joining processes, in order to improve on the quality of the final product. The selection of the manufacturing process for Al and its alloys is based on the capabilities of the specified requirements for components and the alloy used. High pressure die casting (HPDC) is the most widely used casting process in the automotive industry due to its high production rate, and ability to produce complex shaped components. However, HPDC is prone to porosity making it difficult to heat treat and weld. Semi solid metal (SSM) forming has the potential to produce near-net-shape components with high integrity. Due to laminar filling characteristics of SSM HPDC, low porosity or porosity free castings can be produced. This offers the opportunity to apply heat treatment as well as weld the SSM HPDC components. A high continuous wave Nd: YAG laser has been used to investigate the weldability of SSM cast A356 alloy. The CSIR rheo-process was used to prepare the aluminium A356 SSM slurries and thereafter plates (4X80X100 mm3) were cast using a 50 Ton Edgewick HPDC machine. Plates in the as cast, T4 and T6 heat treatment conditions which had passed radiography inspection were then laser welded. Some of the initial as-cast plates that were welded were subjected to pre or post weld T4 or T6 heat treatment and are referred to as pre-weld T4 or pre-weld T6 and post-weld T4 or post-weld T6 specimens.

Includes bibliographical references.

Includes bibliographical references (leaves 96-103).