Mechanical properties of ultra high-purity aluminum

Nanoindentation data reveal interesting behavior in aluminum with various purity levels: 99.9999% (6N), 99.99% (4N), and 99% (2N). Nanoindentation was used to investigate the relationship between the purity level and the mechanical properties of ultra high-purity aluminum at room temperature. The area subjected to nanoindentation would be expected to behave similarly to a perfect, dislocation-free single crystal. Nanoindentation data were also compared with results from conventional tension and hardness tests. These results highlight the differences between microscopic and macroscopic properties. The tensile strength and the hardness of normal-purity aluminum 99% (2N) are greater than those of ultra high-purity aluminum 99.9999% (6N) and high-purity aluminum 99.99% (W. However, in the nanoindentation test, the penetration depth for ultra high-purity aluminum (6N) and high-purity aluminum (4N) is less than that for normal-purity aluminum (2N). Thus, microscopic mechanical properties differ from macroscopic mechanical properties. It is suggested that the surface of high-purity aluminum is harder than that of normal-purity aluminum on the micro scale. The experimental result shows that a perfect crystal is harder than an imperfect crystal. Furthermore, some recovery of the indentation mark was observed in high-purity aluminum, caused by the mobility of defects in the sample.