Orientation of silicon particles in a binary Al–Si alloy

The orientations Si-crystals take in aluminium, in an alloy with composition Al–1.3at%Si, were investigated by transmission electron microscopy. Hardness was measured for isothermal heat-treatments at 175 C and 260 C. Conditions analysed by TEM were 17 h at 175 C and an additional 3 h at 260 C, both containing a high density of small Si-crystals, the finest corresponding to 175 C. Two main orientation relationships were found: ð001ÞAl jj ð001ÞSi; ½100 Al jj ½100 Si and ð001ÞAl jj ð110ÞSi; ½1 1 1 Si jj ½010 Al: The first accounted for approximately 60% of Si precipitates in condition 17 h_175 C. Despite a high number density and well-aligned interfaces, the Si precipitates have negligible influence on hardness. Findings are consistent with Ge particles in Al–Ge alloys.