Development of Aluminum Alloys for Cartridge Cases

The study was aimed at developing an aluminum alloy suitable for use in a 5.56mm cartridge case. Two distinctly different types of properties were required. In the annealed condition, the alloy must have good formability, such that the many cup and draw operations can be readily performed without the introduction of defects. In the final heat treated condition the alloy must exhibit both high strength and toughness. Ideally, a yield strength of 80,000 psi and a tear strength to-yield strength ratio of 1.5 were desired by the Sponsor. Such a combination of properties is not currently available in any known commercial alloy. Variations of the commercail alloys 7075, 7178, and 7001 were studied. The major elements (Zn, Mg, and Cu) were not changed appreciably from commercial practice. The homogeneity of the alloys was varied, primarily by controlling the levels of those elements with quite low solubility in aluminum, viz. Fe, Si, and Mn. Also the effects of two recrystallization retarding elements, Cr and Zr were studied. (Author)