Lots of the available literatures on hafnium in aluminum alloys are reviewed. The new binary Al-Hf phase diagram is simply assessed. Two ternary phase diagrams including Al-Hf-Zr and Al-Hf-Sc are accounted for, with emphasis on the aluminum rich part of the diagrams. The relationship between different structure Al3Hf and several different formation mechanisms including the probable phase transformation mechanisms is described. The continuous Al3Hf phase particles can serve as a grain refiner in the Al melt and a precipitate for controlling the grain structure of the alloy and a strengthening precipitate. A series of effects of Fe, Si, Zr, Sc and Li addition on the behavior of Al3Hf and Al alloys are given. Moreover, the effects of Hf on the microstructure and properties of Al alloys, such as hardness and creep, are reviewed. Finally, some views of Hf-containing Al alloys are summarized.
Zhi-Hong JiaHui-Lan HuangXue-Li WangYuan XingQing Liu
In this study,the morphology,composition and evolution of intermetallics in Al-7Si-0.3Mg,Al-7Si-0.3Mg-0.47Hf,Al-7Si-0.3Mg-0.16 Zr and Al-7Si-0.3Mg-0.14Zr-0.44Hf alloys were characterized by optical microscope(OM),scanning electron microscope(SEM)with energy-dispersive spectrometer(EDS) and transmission electron microscope(TEM).The AlSiZr,AlSiHf and AlSiZrHf phases are formed with additions of Zr and/or Hf in base alloy during solidification,especially the AlZrHf primary particles.The three-dimensional morphology of the AlZrHf particle evolves from 10-polyhedron-like to compressed cube-like during solidification.The new AlZrHf phase experiences partial dissolution after solution treatment,while the others remain in the initial morphology.High Si contents lead to form thermally stable Zr/Hfrich precipitates in Zr/Hf-containing alloys during solution treatment,especially the nanobelt-like Si2Zr,Si2Hf and Si2(Zr,Hf) precipitates.Particular orientation relationships and the growth mechanism are identified.The finding of the work broadens the elevated temperature application of Al-Si-Mg in modern automotive aluminum engine.
Hui-Lan HuangZhi-Hong JiaYuan XingXue-Li WangQing Liu
