Improvement in the effectiveness of diamond as reinforcement in strengthening the porous alumni composite

Abstract

The growing demand for lightweight structures in automotive and aerospace fields has attracted enormous attention to further reduction in weight of aluminium (Al) alloys and composites, that are mostly preferred for such applications. This urge resulted in the development of porous Al. Porous Al is a lightweight material that inherits high strength and stiffness to weight ratio, energy saving and excellent impact energy absorption during collision. However, these are often associated with low density resulting in low mechanical and thermal performance, which might limit its efficiency, design flexibility as well as potential applications. The aim of this research is to improve the strength of porous Al by the inclusion of alloying elements and Ti-coated diamond particles as reinforcements. In this study the powder metallurgy technique was applied due to its near net shape production, flexibility in terms of constituent addition and material conservation capabilities. The alloying elements such as magnesium (Mg), copper (Cu), boron (B), and tin (Sn) were added to the Al matrix to strengthen it and further reinforced with titanium (Ti)-coated diamond particles. The porosities in such composites were achieved by using polymethylmethacrylate (PMMA) particles as space holders. The porous Al composites were developed at varying processing parameters such as sintering temperature, compaction pressure, and sintering time, followed by varying Ti-coated diamond content, PMMA particle content, and PMMA particle size. Further, the compressive properties (plateau strength, and energy absorption capacity) of the resultant porous Al composites were optimized using experimental methodology, Design of experiments (L9 orthogonal array) as well as statistical methodology, analysis of variance (ANOVA). Finally based on the optimum process parameters, PMMA content and PMMA particle size, the porous Al composite with various content (0, 6, 9, 12, 15 and 20 wt.%) of uncoated and Ti-coated diamond particles were studied. Thus, the optimum content of diamond required to enhance the performance of porous Al composite was evaluated. The microstructure of the resultant porous Al composite revealed that the PMMA space holders contributed to well-defined macro pores with good interfacial integrity. In addition to this, the XRD analysis confirmed the presence of strengthening phases as a result of addition of alloying elements. Additionally, Ti-coating improved the interfacial bonding of diamond particles with Al alloy matrix. The results of parameters optimization revealed that the sintering temperature significantly impacted the compressive properties, and the maximum values could be achieved at sintering temperature of 590°C, compaction pressure of 350 MPa, and sintering time of 90 min. On the other hand, the compositional optimization revealed that the diamond content had a major impact on the compressive properties and the enhanced values could be achieved at diamond content of 12 wt. %, PMMA particle size of 150 ?m, and PMMA content of 25 wt. %. The stress strain curves also showed a significant improvement in the compressive properties with nearly ductile behavior. Moreover, the maximum values of plateau strength and energy absorption capacity in the range of (40-45 MPa) and (11.20-13.68 MJ/m3) respectively were achieved for porous composite reinforced with 9-12 wt.% of Ti-coated diamond particles. The results reflected an increment of 61-82% in plateau strength and 54-88% in energy absorption capacity as compared to the unreinforced porous Al. This shows a significant improvement in the strength and energy absorption capacity of porous Al composites on addition of Ti-coated diamond as a reinforcement. This material can be potentially applied as cores material in the sandwich structures to lighten the weight of structures without compromising their strength especially in automotives and aerospace applications.