The effects of nickel additions on the change in microstructure of Zn-xNi lead free solder alloys were investigated. The investigation revealed that increasing Ni additions led to the increase in size of intermetallic Zn-Ni particles along with an increase in volume fraction of intermetallic particles. The microstructure also revealed the presence of the prominent delta (δ) phase in all three compositions of the solder alloy i.e. Zn-0.7 mass% Ni, Zn-1.0 mass% Ni and Zn-1.5 mass% Ni respectively. The presence of irregular shaped δ phase particles and conjoined δ phase particles were noticed in alloys with higher Ni content along with δ particles at grain boundaries. The most remarkable change occurred in the size of Zn grains, which decreased in size as Ni additions were increased. This reduction in size can be attributed to pinning effect of Zn grains by intermetallic particles.
The indentation hardness of Al-SiCp metal-matrix composites synthesized by stir casting process was investigated. Stir casting method was selected as the casting method due to its simplicity, flexibility and applicability. This method allows a conventional metal processing route to be used which minimizes the cost of the product. The silicon carbide particles to be used were first ball milled for size reduction. These particles were then sieved in a mechanical shaker to obtain different particle sizes. SiC particles of size 74µm corresponding to mesh 200 were selected for addition to the Al matrix. The composite was prepared by adding preheated SiC particles to the Aluminium melt via stir casting. Test specimens were prepared by varying the wt% of SiC (1%, 3%, 5%, 7% and 9%). As the SiCp additions were increased, the hardness of the composite increased to a large extent. This can be attributed to the uniform distribution of the SiC particles in the Al matrix via stir casting method.
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