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In this study, an aluminum (Al) alloy matrix reinforced with uncoated and titanium (Ti) -coated diamond were developed using powder metallurgy technique where polymethylmethacrylate (PMMA) particles were employed as space holders. The weight % of uncoated and coated diamond varied as (0, 6, 9, 12, 15, and 20 wt.%). Microstructural and elemental analysis was examined using scanning electron microscopy and energy dispersive spectroscope, respectively. The relative density and porosity that were in the range of 0.72–0.92 and 31–44% respectively, were measured using Archimedes principle. The compressive properties were measured and correlated with microstructure observations. The microstructure of the composite samples revealed presence of well-defined macro pores with good interfacial integrity. The X-ray diffraction revealed the presence of strengthening phases such as Al2Ti, Mg2Sn, AlB12, Cu5Sn6, Al12Mg17 and MgB2 phases formed as a result of addition of metal additives in Al matrix. Further improvement in the strength was obtained by using Ti-coated diamond particles as reinforcement. As Ti formed a good interface between the Al alloy matrix and the diamond thereby preventing the formation of undesirable carbide phases. There was an improvement in plateau stress and energy absorption capacity of 82 and 88% as compared to unreinforced porous sample. The maximum values obtained for the plateau stress and energy absorption capacity were 45.12 MPa and 13.68 MJ/m3 respectively for 9 wt.% of Ti-coated diamond reinforced composites. Uncoated diamond reinforced composites, on the other hand, reduced the strength of porous Al alloy matrix due to the formation of brittle intermetallic compound such as carbides (Al2C3) at the interface. As a result, the coated diamond particle surface modifies and improves the wettability of the Al alloy matrix and diamond interface.

The process of sintering involves applying pressure and heat to the materials without melting them in order to fuse the particles together into a solid mass. The fusion between the particle are also known as interparticles necking which plays an important role in producing high-density products. Increasing in necking size between particles will allow the formation of smaller pore sizes which help to produce stronger and higher hardness materials. The necking also plays an essential role in producing high porosity products that are commonly used for medical applications which still required high tensile value and hardness. For this, proper process parameters were required to produce larger necking growth. To get a better understanding of this matter, the effect of powder and processing parameters will be reviewed in this article. The parameters for different processes such as conventional sintering, microwave sintering, selective laser melting, and others will be discussed in this paper as well.

Porous aluminum (Al) composites are lightweight and high-strength materials composing of Al as a matrix material with some strengthening reinforcements and pore-forming agents that result in the formation of new material with superior physical properties and energy absorption capacities. This work gives an overview of the porous Al-foams developed thus far, including the foaming agents and space holders, their properties, production techniques, and applications. First, it deliberates the foaming agents and space holders responsible for the foaming and formation of pores in the composites followed by the mechanical properties of the foams. Al has huge potential for applications that require lightweight, high-strength, and high-energy absorption capacity materials, especially in structural construction and automobile manufacturing. Although Al-foams have been successfully used in automobiles for crashworthiness, lightweight structure, and other functional applications, the development of Al foams with enhanced characteristics and properties has limitations. This review discusses various reinforcements used for improving the characteristics of Al-foams. This review also provides an overview of various commercial foams and their contribution to several applications. Finally, it attempts to reveal impediments in foam production with suggested solutions for overcoming the problems in this area.