Influences of Increased Pressure Foaming on the Cellular Structure and Compressive Properties of In Situ Al-4.5%Cu-xTiB2 Composite Foams with Different Particle Fraction.

Zhengyi Niu,Zhuokun Cao,Zhibao Jiang,Zhentao An,Yang Yu

doi:10.3390/ma14102612

Abstract

Metallic foams have drawn increasing attention in applications ranging from lightweight structures to energy absorption devices. Mechanical properties of metallic foams depend on both their microstructure and cellular structure. In situ Al-4.5%Cu-xTiB2 composites were used as start materials for fabrication of closed-cell foams through liquid route under atmosphere pressure and increased pressure, aiming at simultaneously strengthening the cell wall material and optimizing the cellular structure. Macro-structural features of the foams were determined by micro X-ray computed tomography (µCT); results exhibit that increasing weight ratio of in situ TiB2 particles leads to coarsened cell structure for foams made under atmosphere pressure, due to the increase in critical thickness of cell wall rupture. Significant reduction of cell size and increase in cell circularity were observed for foams fabricated under increased pressure. Quasi static compression test results indicate that yield strength of foam samples increases with increasing particle fraction and refinement of cell structure. Microstructure observation shows that the continuous network at interdendritic regions consists of in situ TiB2 particles and intermetallic compounds are responsible for the reduced ductility of cell wall materials and the reduction in energy absorption efficiency of foams with high particle fraction. The influences of cell structure on the normalized strength and specific energy absorption were also discussed, and it was found that the improvement of yield strength and energy absorption of composite foams attributes to both the reinforcement of in situ TiB2 particles and the refinement of cellular structure.

Highlights

Metallic foams have received much attention for automobile, aerospace, and structural applications due to their unique combination of light weight, high specific strength and specific stiffness, as well as energy absorption capacity and damping ability [1,2,3]
From the compressive test results, it is found that the yield strength σ* of foam specimens increases with increasing in situ particle fraction, which is in accordance with experimental results of dense composites
In the research work of Mukherjee et al, the structure and property correlation were discussed on three aluminum foams with different structural features, and the results indicate that decrease in cell size and increased circularity of large cells in foams could lead to improvement of mechanical performance [37]

Summary

Introduction

Metallic foams have received much attention for automobile, aerospace, and structural applications due to their unique combination of light weight, high specific strength and specific stiffness, as well as energy absorption capacity and damping ability [1,2,3]. In situ TiB2 particles do not attach to the gas–liquid interface during the foaming process for their good wettability with molten aluminum and their influence on liquid foam stability and mechanical properties of composite foams are not clear yet [12,13]. Kennedy reported an increase in foam expansion and improvement in compressive strength of aluminum foams prepared by applying powder metallurgy route with ex situ TiB2 particles addition [14]. The lack of foam stability and inhomogeneity in cellular structure leads to decrease of compressive strength and energy absorption of A357 alloy-based composite foams when the weight fraction of in situ TiB2 particles increased from 5.0% to 10.0% [17]

Results

Discussion

Conclusion