The structures and compositions of Ti and Zr rich phases in ternary Al-Ti-Zr and quaternary Al-Si-Ti-Zr systems were investigated by energy dispersive spectroscopy and X-ray diffraction.The additions of Ti and Zr were changed.It was found that Ti and Zr can replace each other in the Ti and Zr rich phases of Al-(Si-)Ti-Zr alloys.Compositions of the phases have been measured as a function of Ti and Zr additions.The content of Ti(Zr) in the phases increases with its addition in the alloys.Besides,the increase of Ti content can result in a decrease of lattice parameters.Microhardness of the phases in Al-18Si-xTi-/Zr alloys changes with composition evolution.Moreover,the microhardness is higher than that of the intermetallics of ternary Al-Si-Ti and Al-Si-Zr alloys,due to the distortion of crystal structure caused by the replacement of Ti and Zr.
Al-LaB6 alloy was successfully prepared by aluminum melt reaction method.Microstructure analysis of this alloy was carried out by field emission scanning electron microscopy(FESEM),Raman spectroscopy and transmission electron microscopy(TEM).It was found that cubic LaB6 particles were highly dispersed in aluminum matrix with a uniform edge length of about 4.5 μm.Grain refining potency of LaB6 on commercial pure aluminum was also investigated.It was shown that LaB6 could act as an effective and stable nucleation substrate for α-Al during solidification process,due to their crystallographic similarity.The coarse grains of commercial pure aluminum were obviously refined to small equiaxed ones by addition of 0.5% Al-5LaB6 alloy at 720℃.
The grain refi nement limits of commercial pure Al inoculated by Al-5Ti-1B, Al-5Ti-0.25C and Al-5Ti-0.3C-0.2B master alloys were studied, and the infl uence of melting temperature on the grain refi ning performance of these three master alloys was investigated using a high scope video microscope(HSVM), a fi eld-emission scanning electron microscope(FESEM), an electron probe micro-analyzer(EPMA) and X–ray diffraction(XRD) method. Results show that there is a grain refi nement limit of commercial pure Al refi ned by these three master alloys; with the same addition level of 1.5% under the present experimental conditions, the grain refi nement limits(smallest average grain size) of commercial pure Al refi ned by Al-5Ti-1B, Al-5Ti-0.25C and Al-5Ti-0.3C-0.2B master alloys are 50 μm, 80 μm and 80 μm, respectively. In addition, with an increase in the melting temperature of the pure Al, the grain refi ning performance of Al-5Ti-1B and Al-5Ti-0.25C master alloys decreases, but the grain refi ning performance of Al-5Ti-0.3C-0.2B changes little.
