A study on machining characteristics of strontium modifies LM-6 alloy

Abstract

The eutectic aluminium silicon alloy (LM-6) is known to have poor machinability. This work explains the effect of strontium modification on increasing machinability of LM-6 alloy. Samples of LM-6 alloy were prepared; sand cast, die cast, heat treated, and non-heat treated samples were created in pairs, strontium modified and unmodified, resulting in eight different combinations of LM-6 alloy samples. These samples were put to identical physical and machining tests, their microstructures were photographed using Scanning Electron Microscope (SEM) photography. To remove statistical error, each test was conducted three times. Results showed that strontium addition to LM-6 alloy resulted in refining its microstructure; large silicon flakes in the un-modified LM-6 alloy were transformed into fine and well dispersed globular grains. Also, strontium modified samples produced a 4% reduction in hardness, a 7% increase in ductility and a 36% reduction in average flank wear, thus Strontium addition resulted in improving its machinability. Strontium addition improved machinability of LM-6 alloy by primarily refining its microstructure; reduced grain size of the hard silicon particles resulted in reduction of the abrasive effect on the tool face. Evidence of this can be shown in the fact that dramatic reductions in flank tool wear rate were observed only when the microstructure was refined, furthermore, SEM figures of cutting tools that cut modified samples showed great reduction in abrasive wear.