INVESTIGATION OF EDGE CRACKING PROPENSITY IN COLD-ROLLED COMMERCIAL ALUMINIUM ALLOY 8011 UNDER MIXED OIL LUBRICATION CONDITION

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Department of Engineering

ABSTRACT
The effect of iron content on edge cracking tendency in cold-rolled commercial aluminium alloy 8011 under a mixed coconut/diesel oil (factory formulated oil) lubrication condition and under neem seed oil as an alternative has been investigated. Three different aluminium alloy plates each containing 0.708%Fe, 0.909%Fe and 0.931%Fe were produced by chill casting method. Seven samples each of dimension 240mm x 140mm x 7mm were cast per alloy. As-received commercial aluminium alloy 8011 of 0.857%Fe was cut into seven samples of the same geometry. Experimentation involved cold reduction in thickness by rolling at various degrees of deformation, followed by testing of mechanical properties and qualitative metallographic analysis. Performance evaluation of mixed coconut/diesel oil and neem seed oil lubricants in friction reduction of cold-rolled commercial AA 8011 and proportion of mixture of coconut and diesel oil that will give the highest percentage deformation were also conducted by plane strain compression test. From the results obtained, it was observed that aluminium alloy 8011 generally exhibited softening characteristics as shown by its maximum ultimate tensile strength of 176.45MPa at 60% reduction in thickness and on reaching the peak hardness values, all samples displayed decrease hardness for given levels of percent reduction in thickness. It was also observed that for up to a maximum of 0.931%Fe, AA 8011 could be cold-rolled to a maximum of 60% reduction in thickness without any evidence of edge cracking. Alloys with 0.909%Fe and 0.931%Fe, edge cracked at 70% and 80% reductions in thickness and the other alloys showed no edge cracking for the whole percentage deformations investigated. Furthermore, samples of AA 8011 containing more than 0.9%Fe revealed higher tensile strength when cold-rolled to 80% reduction in thickness. The results of plane strain compression test showed that at any specific load, neem seed oil provided better lubrication; about 106% reduction in thickness better than mixed coconut/diesel oil at100kN load. The mixture of locally sourced coconut and diesel oil in different proportions performed best in friction reduction at the ratio of 30% coconut oil and 70% diesel.