In situ tempering of melt spun AlGeSi-foils

Abstract

AlGeSi-alloys of different composition were cast by a melt spin device to ribbons of 40 μm thickness. The ribbons melt near 500 °C and should be well suited for brazing of high strength Al-alloys. Because of the existence of metastable phases, these ribbons are brittle in the rapidly solidified state, but increasingly ductile and cuttable after an appropriate annealing between 200 and 400 °C. The thermally induced phase transformations are revealed by the hightemperature X-ray diffractograph as well as, with help of a heating sample holder, by the analytical transmission electron microscope (TEM). The identification of elements and phases is performed by X-ray Bragg reflexes and of electron diffraction (ED) patterns, whereby the latter can be associated to single microstructure details in the sub-μm range. Moreover, the distribution of the elements can be seen on distribution maps “din the light” of characteristic X-ray spectral lines.

The observed microstructure of as-quenched AlGe45 with 2 or 4 mass-% Si was of similar appearence but more refined as in the AlGe45 alloy. It consists of α-Al primary crystals surrounded by an eutectic mixture of α-Al and two metastable intermetallic AlGe(Si) phases. Si was observed exclusively within these metastable phases. During an appropriate tempering the metastable phases transform into the equilibrium phases α-Al and β-Ge(Si). For this decomposition the temperature is decreased by alloying with Si.