Refinement and thermal analysis of hypereutectic Al 25%Si alloy were investigated with scanning electron microscope (SEM) and differential scanning calorimeter (DSC). The results show that the average size of primary ...Refinement and thermal analysis of hypereutectic Al 25%Si alloy were investigated with scanning electron microscope (SEM) and differential scanning calorimeter (DSC). The results show that the average size of primary silicon in Al 25%Si alloy without and with phosphorus addition are 250 μm and 30 μm, respectively. But the primary and eutectic growth temperature is raised by about 17.3 ℃ and 4?℃ respectively due to phosphorus addition. The primary nucleation temperatures are 745.0 ℃ and 762.0 ℃ for untreated and treated samples and in addition, the enthalpy changes of primary and eutectic transformation are -261.0 J/g and -397.3 J/g without phosphorus addition, -294.2 J/g and -386.1 J/g with phosphorus addition, respectively. Otherwise the mechanisms of refinement and thermal transformation of Al 25%Si alloy in solidifying process are also discussed. [展开更多
To improve the wear resistance of cast Al?17Si?5Cu alloy(AR alloy),isothermal heat treatment is employed to modify the morphology of Si particles(particularly eutectic Si particles).Furthermore,wear behaviour of heat-...To improve the wear resistance of cast Al?17Si?5Cu alloy(AR alloy),isothermal heat treatment is employed to modify the morphology of Si particles(particularly eutectic Si particles).Furthermore,wear behaviour of heat-treated alloy(HT alloy)along with AR alloy is studied using a pin-on-disc tribometer.Worn surfaces are then characterised using scanning electron microscope.The result reveals considerable microstructural modifications after the heat treatment.Accordingly,higher hardness value in HT alloy is obtained compared with AR alloy.The overall wear rate for HT alloy is found to be significantly lower compared with AR alloy at all the applied loads,indicating remarkable improvement in wear resistance.Eutectic Si particles become from acicular/rod-like to spherical/equiaxed morphology(aspect ratio close to 1)on heat treatment,resulting in good bonding with the matrix.Thus,they remain intact during wear and being harder,providing resistance to wear.Moreover,the increased hardness on heat treatment causes further resistance to wear.Therefore,the combined effect of intact harder Si particles on the wearing surface and higher hardness results in superior wear behavior in HT alloy at all loads compared with AR alloy.展开更多
Hypereutectic Al -27Si alloys were joined without flux by ultrasonic-assisted soldering at 420 ℃ in air using Zn -5Al the filler alloys, and Si particulate-reinforced Zn - Al based composites filler joints were obtai...Hypereutectic Al -27Si alloys were joined without flux by ultrasonic-assisted soldering at 420 ℃ in air using Zn -5Al the filler alloys, and Si particulate-reinforced Zn - Al based composites filler joints were obtained. The ultrasonic vibration introduced into soldering could influence the migration of Si particles and the microstructure of solidified Zn - Al based alloys. Both the distribution of Si particles and microstructure of the solidified Zn - Al based alloys affected the shear strength of joints. The shear strength increased with the ultrasonic vibration time. The highest average shear strength of joints reached to -68.5 MPa. Transcrystalline rupture mode was observed on the fracture surface.展开更多
文摘Refinement and thermal analysis of hypereutectic Al 25%Si alloy were investigated with scanning electron microscope (SEM) and differential scanning calorimeter (DSC). The results show that the average size of primary silicon in Al 25%Si alloy without and with phosphorus addition are 250 μm and 30 μm, respectively. But the primary and eutectic growth temperature is raised by about 17.3 ℃ and 4?℃ respectively due to phosphorus addition. The primary nucleation temperatures are 745.0 ℃ and 762.0 ℃ for untreated and treated samples and in addition, the enthalpy changes of primary and eutectic transformation are -261.0 J/g and -397.3 J/g without phosphorus addition, -294.2 J/g and -386.1 J/g with phosphorus addition, respectively. Otherwise the mechanisms of refinement and thermal transformation of Al 25%Si alloy in solidifying process are also discussed. [
基金DST-SERB grant, vide Project No. YSS/2014/000172 dated 2015-08-17
文摘To improve the wear resistance of cast Al?17Si?5Cu alloy(AR alloy),isothermal heat treatment is employed to modify the morphology of Si particles(particularly eutectic Si particles).Furthermore,wear behaviour of heat-treated alloy(HT alloy)along with AR alloy is studied using a pin-on-disc tribometer.Worn surfaces are then characterised using scanning electron microscope.The result reveals considerable microstructural modifications after the heat treatment.Accordingly,higher hardness value in HT alloy is obtained compared with AR alloy.The overall wear rate for HT alloy is found to be significantly lower compared with AR alloy at all the applied loads,indicating remarkable improvement in wear resistance.Eutectic Si particles become from acicular/rod-like to spherical/equiaxed morphology(aspect ratio close to 1)on heat treatment,resulting in good bonding with the matrix.Thus,they remain intact during wear and being harder,providing resistance to wear.Moreover,the increased hardness on heat treatment causes further resistance to wear.Therefore,the combined effect of intact harder Si particles on the wearing surface and higher hardness results in superior wear behavior in HT alloy at all loads compared with AR alloy.
基金sponsored by the National Natural Science Foundation of China(Grant No.51504165)the Project funded by the China Postdoctoral Science Foundation(Grant No.2016M601271)Tianjin Scince&Technology Project(Grant No.16JCQNJC02600)
文摘Hypereutectic Al -27Si alloys were joined without flux by ultrasonic-assisted soldering at 420 ℃ in air using Zn -5Al the filler alloys, and Si particulate-reinforced Zn - Al based composites filler joints were obtained. The ultrasonic vibration introduced into soldering could influence the migration of Si particles and the microstructure of solidified Zn - Al based alloys. Both the distribution of Si particles and microstructure of the solidified Zn - Al based alloys affected the shear strength of joints. The shear strength increased with the ultrasonic vibration time. The highest average shear strength of joints reached to -68.5 MPa. Transcrystalline rupture mode was observed on the fracture surface.
