THERMAL FATIGUE RESISTACES OF 356 A D 4 3 CAST AI ALLOYS

Til rmal f atigue is a stochas tic process often showing considerable scatter e~'('n incontrolled en ironments. due to complexity 0/ thermal fatigue, there is no a complete analyticalsolution tor p redicting the effect 0/ this property on the life 0/ various comp onents, subjected tosevere thermal fluct uations. among these components, one can mention car cylinder; cylinder headand piston which bear damages due to thermal fa tigue. all these components are usually producedb ' casting technique i ii order to comprehend and compare the thermal fa tigue res l: lance of castai alloys 356 atu] 413, this research was designed and performed. for this pu rp ose, s veralsamples 111 the fo rm ofdisc were cast from the two alloys in sand mould. the -microstructures ofthecast samples were studied by light microscopy in order to choose the samp les with the leastamounts of defects f or thermal fa tigue tests. the results 0/ thermal fa tigue tests showed that thenucleation ofmicrocracks in ai-356 alloy occurred at shorter time relative to those occurred in ..114j3allov under tile same test conditions. in addition, the density 0/micro-crack in ai-356 alloyw{1.'i more titan that 0/ ai- lj alloy, the results 0/froctography on 356 alloy indicated that thecracks 'ere generally nucleated from inter-dendritic shrinkage porosities and occasionullv [ramrile illter {ice 0/ silicon pa rticles with the matrix. the growth 0/ these micro cracks was along thedendrite arms. fro tography 0/413 alloy fracture surfaces showed that nucleation ofmicrocracksi1'ils often associated with silicon particles. thermal fatigue, inter-dendritic fracture, silicon particles, al-allov, microcracks, al356, ai 413