Evolution of microstructure and mechanical properties of A356 aluminium alloy processed by hot spinning process

The evolution of microstructure and mechanical properties of A356 aluminum alloy subjected to hot spinning process has been investigated. The results indicated that the deformation process homogenized microstructure and improved mechanical properties of the A356 aluminum alloy. During the hot spinning process, eutectic Si particles and Fe-rich phases were fragmented, and porosities were eliminated. In addition, recrystallization of Al matrix and precipitation of Al Si Ti phases occurred. The mechanical property testing results indicated that there was a significant increase of ductility and a decrease of average microhardness in deformed alloy over die-cast alloy. This is attributed to uniform distribution of finer spherical eutectic Si particles, the elimination of casting defects and to the recrystallized finer grain structure.

Effect of holding pressure on density and cooling rate of cast Al-Si alloy during additive pressure casting

The cast Al-Si alloy was fabricated using the Additive Pressure Casting(APC)method.The effects of holding pressure from 50 to 400 k Pa on the density,cooling rate,and mechanical properties of the alloy,and the corresponding mechanism were discussed.The results indicate that the application of high holding pressure(300 k Pa)enhances the feeding ability of the alloy,leading to an increase of the density.Meanwhile,the cooling rate of the alloy is increased by 100%.In addition,the tensile testing results show that the increase of holding pressure from 50 to 300 k Pa improves the tensile strength and elongation of the alloy by 6.2%and 81.3%,respectively.However,excessive holding pressure(400 k Pa)might lower the density and cooling rate of the alloy due to the feeding channels being blocked.

Mechanisms of reactive element Y on the purification of K4169 superalloy during vacuum induction melting

The effects of rare earth element Y on the purification of K4169 superalloy during vacuum induction melting were investigated at different superheating temperatures. The corresponding interaction mechanisms were also clarified. Results showed that the addition of Y remarkably promoted the purification effect on the K4169 melt. The contents of O and S in the K4169 as-cast alloy ingots after purification were 3–4 and 8–10 ppm, respectively. The degrees of deoxidation and desulfurization increased to 50% and 57%, respectively, upon the addition of 0.1 wt% Y. The yttrium-rich phase that precipitated at the grain boundary blocked the diffusion of C and the accumulation of S, thereby contributing to the purification of the alloy.

Effect of La addition on microstructure and mechanical properties of hypoeutectic Al-7Si aluminum alloy

The effect of La addition(0,0.1,0.2,0.4,wt.%)on the microstructure,tensile properties and fracture behavior of Al-7Si alloy was investigated systematically.It is found that the La appears in the Al-7Si alloy in the form of Al4La and Al2Si2La phases.La addition can refine the secondary dendrite arm spacing(SDAS)and eutectic Si particles,which are decreased by 7.9%and 7%,respectively,with the optimal La content of 0.1wt.%.Because when 0.1wt.%La is added,a relatively higher nucleation undercooling of 37.47℃ is observed.Higher undercooling degree suggests that nucleation is accelerated and subsequent growth is restrained.After T6 heat treatment,compared with the without La,the ultimate tensile strength of the alloy with 0.1wt.%La is enhanced by 5.2%from 333 MPa to 350.2 MPa and the elongation increases by 73%from 7.37%to 12.75%,correspondingly.The fracture mode evolves from the ductile-brittle mixed fracture to ductile fracture mode.However,when La element content reaches a certain value of 0.4wt.%,serious segregation takes place during the solidification process.The formed brittle phases deteriorate the tensile properties of the alloy and the fracture mode of Al-7Si-0.2/0.4 La changes to mixed ductile-brittle fracture mode.

Cooling Rate Sensitivity of RE-Containing Grain Refiner and Its Impact on the Microstructure and Mechanical Properties of A356 Alloy

The cooling rate sensitivities of A1TiB, RE and A1TiB-RE refiners were investigated using laboratory experiments and the actual industrial applications of A356 automotive wheel via low pressure die casting technology. Their impact mechanisms on the microstructure and mechanical properties of the A356 alloy were discussed. The results demonstrated that the AITiB-RE refiner possessed most effective and synergetic refinement effects compared to the individual A1TiB or RE refiners. The A1TiB-RE refiner exhibited the least sensitivity to the cooling rate changes than the other refiners. The comprehensive properties of alloy wheel refined by the A1TiB-RE refiner were improved significantly. The tensile strength, yield strength, and elongation of wheel spoke improved by approximately 11.3%, 10.8% and 44.1%, respectively. The property difference values of the tensile strength, yield strength, and elongation in different positions of the wheel decreased from 14.8%, 31.2% and 47.7% to 8.6%, 27.1% and 30.9%, respectively.

Effect of Trace O Element on High-temperature Wettability Between Ni_3Al Melt and Y_2O_3 Ceramic

Effect of trace O element on the high-temperature wettability between Ni3Al scrap melt and Y2O3 ceramic at 1873 K is investigated. With the increase in O content in Ni3Al scrap melt from 6 to 21 ppm, the equilibrium contact angle decreases from 93.3° to 88.9°. The initial surface tension and adhesive work of molten Ni3Al scrap drop from 3153.5 to 807.4 mN m^-1 and from 2974.6 to 882.2 mN m^-1, respectively. The average spreading rate increases from 0.03° s^-1 to 0.17° s^-1. The whole wetting processes are divided into four periods. The main driving force for spreading in period（1） is the adsorption and diffusion of active atoms around the interface. Trace O content in Ni3Al scrap has a significant impact on interfacial reactions which mostly take place in the second stage, and can accelerate the spreading process on Y2O3 substrate. The reaction products during wetting process are Y3Al5O12, YAlO3 and Al2O3.

Microstructure and High-Temperature Oxidation Behavior of Dy-Doped Nb–Si-Based Alloys

Microstructures and oxidation behaviors of four Dy-doped Nb-Si-based alloys at 1250 ℃ were investigated. The nominal compositions of the four alloys are Nb-15Si-24Ti-4Cr-2Al-2Hf-xDy （at.%）, where x = 0, 0.05, 0.10 and 0.15, respectively. Results showed that the four alloys all consisted of Nbss, αNbsSi3 and γNbsSi3, and the addition of Dy produced no obvious effect on the phase constitution and the microstructures of Nb-Si-based alloys. After oxidation at 1250 ℃ for 58 h, it was found that the addition of Dy accelerated the oxidation rate of Nb-Si-based alloys and caused a larger weight gain, accompanied by the formation of a more porous and less protective oxide scale. The oxides of Nb2O5, Ti2Nb10O29, TiNb2O7, Ti0.4Cr0.3Nb0.302 and glassy SiO2 were formed on Dy-doped Nb-Si-based alloys. The high- temperature oxidation mechanism of Dy-doped Nb-Si-based alloys was discussed.

Effect of Open Porosity of Y2O3 Ceramic on the Apparent Contact Angles and Interactions Between Ti47Al Alloys and Y2O3 Ceramic

The effect of open porosity of Y2O3ceramic on the apparent contact angle and interaction between molten Ti47 Al alloy and Y2O3ceramic substrates under pure Ar was investigated by using a sessile drop method at 1600 °C. As the open porosity increased from 9.6% to 30.3%, the spreading rate of molten Ti47 Al alloys on Y2O3ceramic substrates reduced from 2.3 to 1.1°/s; meanwhile, the final equilibrium contact angles increased from 55.8° to 63.6°. The microstructure observations revealed that with increasing the open porosity of the Y2O3substrates, the thickness of sand adhesion at the interfaces of the alloy droplets increased from 5.4 to 15.7 lm, and ceramic particles in the alloy matrix increased as well. The increasing contact area between the molten alloy and the substrate played a dominant role in determining the interaction on Ti Al/Y2O3interface.

Mechanism of yttrium in deep desulfurization of NiCoCrAIY alloy during vacuum induction melting process

In this study,yttrium as desulfurizer on the purification of Ni-20Co-20Cr-10Al-Y alloy during vac-uum induction melting(VIM)process using Y_(2)O_(3)cru-cibles was investigated experimentally.It is found that Y plays an important role on the desulfurizing of the NiCo-CrAIY alloy.Without any addition of Y,merely the employment of Y_(2)O_(3)crucibles could effectively reduce S content of the alloy melts from 28×10^(-6)to 6×10^(-6)-7×10^(-6).With addition of 0.8 wt%Y in the alloy,the concentration of S could further reduce 2×10^(7)3×10^(-6).The primary interactive mechanism between Y and molten alloy was concluded to be the synthesis reac-tion of NisY phase,Y2S3 phases and YAIO_(3)phase.In the desulfurize slags,Y2S3 phases and Y_(2)O_(3)phase are found.No secondary contamination is present in the alloy melts after addition of Y.