Ductile Nature of Aluminum Alloys

Correlations Density Mechanical Properties Porous Alloys
In the recent years, various developments have been made concerning the manufacturing methods used in the production of foams from aluminum alloys. The results of various tests conducted indicate that closed cell powder-route aluminum foams are among the strongest and stiffest commercial aluminum foams in the market. Additionally, the tests showed that aluminum foams have low density and are attractive in that they are attractive materials for the cores of sandwich tubes, shells, and panels (Mccullough et al. 2323). Aluminum foams have many other desiring properties including good electrical conductivity, high-energy absorption, high fire retardance, relatively low thermal conductivity, and high acoustic damping. The main aim of this research study was to determine comprehensive and tensile properties of aluminum closed cell foams and interpreting the properties in relation cell wall and microstructure properties.

The materials used in the study were flat plates of aluminum foams, which were supplied by Mepura Limited. The densities of the plates supplied were ranging from 0.1 to 0.5. The focus of the study was to determine the effect of composition and foam density on the comprehensive properties and the tensile. The dense skin of the materials was removed using wire electro-discharge machining. For comprehension and tension tests, dogbone specimens were used further compression tests were performed using smaller cuboid specimens (Mccullough et al. 2324). Tension specimens and dogbone were cut in both longitudinal and transverse directions to investigate the degree of anisotropy. Comprehensive and tensile tests were conducted at a room temperature where the servo-hydraulic mechanical testing machine was used. To minimize the friction between the platens and specimen, comprehensive loading platens were lubricated using PTFE spray.

The results indicated that comprehensive and tensile yield strengths were approximately equal. It was found that comprehensive dogbone specimens used gave accurate values for the modulus and yielded strength, but it provides limited information on the subsequent comprehensive responses. It was concluded that the stress concentration within the foams led to early yielding, as indicated in the isolated locations (Mccullough et al. 2325). The stiffness and the strength of the foam through the thickness and in the transverse directions were approximately equal to that in the longitudinal direction. Such anisotropy is because of the cells within the foam are ellipsoidal shaped. The elastic modulus and density of the cell wall material are deemed as those of the aluminum alloys.

In conclusion, a ductile behavior was observed in comprehension while in tension aluminum, it behaved in a semi-brittle fashion. Unloading modulus and yield strength were equal in compression and tension, and an increase in non-linearly with relative density was observed. Low silicon content produces stronger and stiffer foam (Mccullough et al. 2329). In both compression and tension, the yields from the foams were almost immediately upon loading, which in greater unloading modulus as compared to the slope of the initial loading line. Aluminum foam is anisotropic, as it yields unloading modulus and strength through the thickness and in the transverse directions, which were approximately equal to those in the longitudinal directions.

It is inhomogeneous because the manufacturing process created weak oxide interfaces with the regions of low-density foams adjacent to such interfaces. Additionally, the cell faces of the manufacturing process are relatively thin and highly defective, as they fail at the low applied strain, and the consequent aluminum foam has properties close to those of the open cell foam. The scatter results in the study indicated the presents of imperfections within the foams (Mccullough et al. 2330). The imperfections include; cell faces containing cracks and voids, weak oxide interfaces, and non-uniform density. It shows that despite the fact that aluminum foam has occupied wide market, it has some weaknesses, which might discourage the consumers unless the manufacturer improves on such imperfections and weaknesses.

Work Cited

McCullough, K. Y. G., N. A. Fleck, and M. F. Ashby. "Uniaxial stress -- strain behaviour of aluminum alloy foams." Acta Materialia 47.8 (1999): 2323-2330.