Composites such as metal matrix composites are being used increasingly because of their desirable properties. In this investigation physical and mechanical properties and microstructures of commercially pure aluminium base composites with varying weight percents of short steel fiber reinforcements with and without Ni-P coating have been studied. The above properties for Al-4.5%Cu base composites with varying weight percent of Ni-P coated short steel fibers as reinforcement have been evaluated too. Using the electroless method, the fibers were coated with Ni-P coating for improvement the wettability between them and aluminium melting and inhibition of formation of detrimental chemical reactions at interfaces that may form harmful intermetalic phases like FeAl 3 and Fe 2 Al 5 . The uniform thickness of coating is one of the advantages of electroless plating. Al-Fe composites with varying weight percent of steel fibers were prepared through liquid process vortex method in a low carbon steel die (St37). During this process the short steel fibers were added to a melting that was being stirred with a graphite stirrer. The low carbon steel die was pre-heated to 500 °C. The melting was prepared in a resistance furnace and the temperature of melting during the vortex process was fixed at 710 °C. Physical and mechanical properties and microstructures of the pure aluminium matrix composites with 3, 6 and 9 weight percent of short steel fibers with and without Ni-P coating were compared with pure commercial aluminium. In Al-4.5%Cu matrix composites with the same weight percent of Ni-P coated short steel fibers, these properties were compared with Al-4.5%Cu castings. According to the results, in the composites with Ni-P coated short steel fiber reinforcements when the weight percent of fibers increased, hardness and density increased and elongation decreased. In these composites the hardness of composite with 9 weight percent of coated short steel fibers is more than 2.5 times of pure aluminium hardness and the strength of these composites in 6 weight percent of coated steel fibers is Maximum. The distribution of fibers is nearly uniform in this type of composites. In pure aluminium matrix composites with uncoated steel fibers, the physical and mechanical properties are less than composites with coated steel fibers and more than pure aluminium castings and the distribution of fibers in matrices is not uniform. In Al-4.5%Cu matrix composites the mechanical properties have been decreased instead of improvement.
