Studies On Fabrication And Compressive Properties Of Aluminum Composite Foams

Aluminum foam has broad application prospects in the construction and transportation industry and especially in the automotive, aerospace industry due to its excellent properties such as lightweight, good sound insulation and sound absorption, energy absorption, damping, thermal insulation and electromagnetic shielding, etc. With the commercial production of aluminum foams, its application gradually spread into many fields. The insufficient strength of aluminum alloy foam has been exposed. Aluminum composites possess many superior performances, such as high specific strength and stiffness, large elasticity modulus, good resistance to abrasion and low thermal expansion coefficient, etc. Thus aluminum composite foams have attracted widespread attention of researchers with potential to improve the strength of aluminum foam.At first, the fabrication process of pure aluminum matrix foam by melt foaming was studied. Through preheat treatment of TiH2, regulation of Ca addition and stirring parameters, control of foaming temperature and time, samples with uniform pores were successfully prepared. The mechanism of Ca addition on increasing viscosity of Al melt and quasi-static compression performance of specimens were studied. The results show that viscosity of Al-Ca alloy melt is related to the dispersive distribution of fine Al+Al4Ca eutectic structures and composite Al-Ca-0oxides thin film. The compression curves of samples displays three-stage characteristics, namely, elastic deformation stage, stress plateau and densification stage. On the whole, the compressive strength and plateau stress of specimens increase with their density. However, due to local large pores of low-density specimens, their compressive strength varies anomaly with density. Local large pores rupture easily during compression and cause fluctuation in stress plateau area.Then with SiCp/Al composites as foam substrate, through Mg addition into melt and high-temperature preheat treatment of SiC particles, melt on the wettability of SiC particles improved and foam specimens fabricated by melt foaming method. Quasi-static compression test of specimens proceeded and microstructure of cell walls was observed. The results show that SiCp/AlSi10Mg composite is too brittle as foam matrix and pores collapse easily. Compared with pure aluminum matrix foam, the compressive strength of SiCp/Al-5wt.%Mg composite foam is higher, the compressive strength of SiCp/AlSi10Mg composite foam is lower. It is SiC particles distribute on the boundary between pores and cell walls that indicates that SiC particles distribute on liquid-gas interface during foaming process, hinder liquid drainage and growth of the bubbles and increase the stability of pores. The different microstructures of cell walls are the root cause of the pore structure and compressive strength difference between two kinds of specimens.In addition, in-situ Mg2Si/Al composite as foam matrix and CaCO3as blowing agent, AI-10wt.%Mg2Si and Al-15wt.%Mg2Si composite foams with uniform pores were prepared. Quasi-static compression test and artificial aging heat treatment of specimens proceeded and microstructure of cell walls was observed. The results show that pores of the specimens are small and uniform. The quasi-static compressive curves of both kinds of specimens follow typical behavior of metal foams with three-stage characteristic during compression and the compressive strength and plateau stress increase with their density. Serrations in stress plateau of compressive stress-strain curves exposed brittle fracture characteristics of cell walls. Through artificial aging heat treatment, the compressive strength and the plateau stress of samples increased remarkably. Thick pseudo-eutectic Al+Mg2Si structures in cell walls split aluminum matrix, caused brittle rupture of cell walls and lowered compressive strength of samples.