Effects of Additional Elements on Microstructure and Precipitation Behaviour in Rapidly Solidified Al-Ti Base Alloys

Rapidly solidified Al-Ti base alloys were prepared by melt spinning at the cooling rate about 107 K/s. The melt-spun ribbons were used to observe the dricrostructures after heat treatment.In the supersaturated Al-Tl-Si alloy, age hardening occurred after 1 h anneal in the temperature range of 4000~500℃, which seems to be attributed to the precipitation of metastable Ll2- (Al,Si)3Ti phase. However. the microhardness was relatively low because of the low v/o and the insufflcient stability of precipitates. Thus. Cr was added to Al-Ti-Si alloys in order to stabilize the microstructures and to increase the v/o of precipitate5. As a result. the alIoys containing Cr were evaluated to possess the improved properties at the service temperature.

Electronic Structure Effect on Model Cluster for L1_2 Structure of Al_3Ti Intermetallic Compound with an Addition of Alloying Elements Fe, Ni and Cu

By use of self-consistent field Xα scattered-wave (SCF-Xα-SW) method, the electronic structure was calculated for four models of Ti4Al14X (X=Al, Fe, Ni and Cu) clusters. The Ti4Al14X cluster was developed based on L12 Al3Ti-base intermetallic compound. The results are presented using the density of states (DOS) and one-electron properties, such as relative binding tendency between the atom and the model cluster, and hybrid bonding tendency between the alloying element and the host atoms. By comparing the four models of Ti4Al14X cluster, the effect of the Fe, Ni or Cu atom on the physical properties of Al3Ti-based L12 intermetallic compounds is analyzed. The results indicate that the addition of the Fe, Ni or Cu atom intensifies the relative binding tendency between Ti atom and Ti4Al14X cluster. It was found that the Fermi level (EF) lies in a maximum in the DOS for Ti4Al14Al cluster; on the contrary, the EF comes near a minimum tn the DOS for Ti4Al14X (X=Fe, Ni and Cu) cluster. Thus the L12 crystal structure for binary Al3Ti alloy is unstable, and the addition of the Fe, Ni or Cu atom to Al3Ti is benefical to stabilize L12 crystal structure. The calculation also shows that the Fe, Ni or Cu atom strengthens the hybrid bonding tendency between the central atom and the host atoms for Ti4Al14X cluster and thereby may lead to the constriction of the lattice of Al3Ti-base intermetallic compounds.

Effects of Sc, Zr and Tion the microstructure and properties of Al alloys with high Mg content

The effects of trace Sc, Zr, and Ti on the microstructure and hardness of A1 alloys with high Mg content （Al-6Mg, Al-8Mg, and Al-10Mg） were studied by optical microscope, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, and Brinell hardness. The grain size of the as-cast alloys was refined by the addition of Sc and Zr, and it was further refined by the addition of Ti. With the same contents of Sc, Zr, and Ti, an increase in Mg content was beneficial to the refinement due to the solution of Mg into α-Al. The refined microstructures of the as-cast alloys were favorable for Brinell hardness. Addition of Sc, Zr, and Ti to the Al-10Mg alloy results in the improvement of peak hardness and it is about 45% higher than that of the Al-10Mg alloy, which is due to fine precipitations of Al3（SC1-xZrx）, Al3（Sc1-xTix）, and Al3（Sc1-x-yZrxTiy）.

Gaseous and electrochemical hydrogen storage behaviors of nanocrystalline and amorphous Nd-added Mg_2Ni-type alloys

Melt spinning technology was used to prepare the Mg2Ni-type(Mg24Ni10Cu2)100-xNdx(x = 0, 5, 10, 15,20) alloys in order to obtain a nanocrystalline and amorphous structure.The effects of the spinning rate on the structures and gaseous and electrochemical hydrogen storage behaviors of the alloys were investigated.The analysis of X-ray diffraction(XRD), transmission electron microscope(TEM), and scanning electron microscope(SEM) linked with energy-dispersive spectroscopy(EDS)reveals that all the as-cast alloys hold a multiphase structure, involving the main phase Mg2 Ni and some secondary phases such as Mg6 Ni, Nd5Mg41, and Nd Ni.The as-spun Nd-free alloy displays an entire nanocrystalline structure,whereas the as-spun Nd-added alloys hold a nanocrystalline and amorphous structure, and the amorphization degree visibly increases with the spinning rate increasing.The melt spinning ameliorates the hydrogen storage performances of the alloys dramatically.When the spinning rate rises from 0(the as-cast was defined as the spinning rate of 0 m s-1) to 40 m s-1, the discharge capacity increases from 86.4 to 452.8 m Ah g-1, the S20(the capacity maintain rate at 20 th cycle) value increases from53.2 % to 89.7 %, the hydrogen absorption saturation ratio(Ra5, a ratio of the hydrogen absorption quantity in 5 min to the saturated hydrogen absorption capacity) increases from36.9 % to 91.5 %, and the hydrogen desorption ratio(Rd10,a ratio of the hydrogen desorption quantity in 10 min to the saturated hydrogen absorption capacity) increases from16.4 % to 47.7 % for the(x = 10) alloy, respectively.