Abstract
It was known that cast 50-ton beta brass (containing about 5 per cent aluminium and 1-2 per cent each of Iron and manganese) was especially susceptible to intercrystalline failure under tensile stress while in contact with sea water or 3 per cent sodium chloride solution. The primary object of the present research was to determine the Influence of aluminium on the intercrystalline weakness. A range of sand cast 40-ton beta brasses, containing from nil to 4 per cent aluminium, was tested. The alloys of low aluminium content contained additions of iron and manganese, and In a few cases, of nickel and tin, In order to give the desired tensile strength. A binary beta alloy and the 50-ton material were included in the tests. Although in specific cases the results were inconsistent, rapid intercrystalline failure in salt solution under sustained stress, of the order of the 0.1 per cent proof stress or higher, occurred only in the alloys containing 3.4 and 4 per cent aluminium and the 50-ton brass with 5 per cent aluminium. Intercrystalline failures also occurred In the susceptible alloys at high sustained stresses in air. The 4 per cent aluminium brass was most susceptible to intercrystalline cracking in air, there being little difference from behaviour in salt solution, and cracking was not prevented by immersing the specimen in liquid paraffin or machine oil, or by coating with plastic. The weakness in the high aluminium alloys was indicated by low results and intercrystalline fractures in ordinary tensile tests with the specimens immersed in salt solution. It was concluded that aluminium was responsible for the intercrystalline weakness, causing a condition of brittleness subject to aggravation by corrosion, although micro-examination gave no information to explain the brittleness. There was evidence that co-presence of Iron and manganese opposed the weakness.