Analysis of an Aluminium Alloy Containing Trace Elements

The microstructure of an Al–Si–Mn–Fe alloy was determined using SEM and Tof-SIMS. The trace elements detected were chlorides and a minute content of fluorides. Potassium was found in large cracks along boundaries. Sn was found on the surface of α-Al(Mn,Fe)Si, on grain boundaries and as separate particles. Small Pb-Sn particles were detected close to grain boundaries. The α-Al(Mn,Fe)Si-particles were 1–5 μm in size and gave pronounced Mn- and Fe-peaks in Tof-SIMS, while silicon did not. SEM-analysis showed that the phase had the composition (wt%): 59Al-12Si-17Mn-12Fe. Separate Tof-SIMS analyses of the matrix and these particles showed that the particles were sputtered at a slower rate than the matrix. The sensitivity factor (S x/Al ) was lower in the particles as compared to the matrix. These observations were explained by the fact that intermetallic phases are substantially harder that the Al-matrix, and that the Si-atoms and a fraction of the Mn and Fe atoms are covalently bonded in α-Al(Mn,Fe)Si-particles.