The effects of isothermal holding time on the semisolid microstructure of Mg-9Al-1Si(mass fraction,%)alloy were investigated.The research results indicate that the Mg-9Al-1Si alloy with non-dendritic microstructure ca...The effects of isothermal holding time on the semisolid microstructure of Mg-9Al-1Si(mass fraction,%)alloy were investigated.The research results indicate that the Mg-9Al-1Si alloy with non-dendritic microstructure can be produced by the semi-solid isothermal heat treatment.With holding time varying from 5 to 30 min,the volume fraction of liquid is gradually enlarged from 29.3%to 38.6%,the morphology ofα-Mg grains changes from initial dendritic shape to spherical types and their average sizes increases from 41.1 to 56.1μm.In addition,during the isothermal heat treatment,the eutectic Mg2Si phase changes from the initial Chinese script shape to granule and/or polygon shape in Mg-9Al-1Si alloy.The modification of Mg2Si phase is possibly attributed to a shift of the eutectic composition of the liquid in semi-solid slurries,towards lower silicon contents with increasing Al content due to a redistribution of Al during isothermal heat treatment.展开更多
Microengines are regarded as the potential replacements for batteries.Aimed at the unsatisfactory thermal property of silicon used in the combustion chambers,ceramics are chosen as the construction material in this pa...Microengines are regarded as the potential replacements for batteries.Aimed at the unsatisfactory thermal property of silicon used in the combustion chambers,ceramics are chosen as the construction material in this paper.The fabrication process where alumina has been chosen as the microengine material is discussed.Vigorous FEA has been carried out,and it is found that the material satisfies the stress and deformation requirements of the design.Then the alumina fabrication process is described.Soft reusable polydimethylsiloxane(PDMS)moulds are produced from SU-8 resist masters,and alumina microengine parts are produced using the PDMS moulds.Images of the ceramic components show that the fabrication satisfies the design requirements.展开更多
The anodizing parameters of voltage, current density, temperature, and electrolyte choice were assessed to find an appropriate combination for the superheated slurry cast 7075 Al alloy substrate.The alloy was anodized...The anodizing parameters of voltage, current density, temperature, and electrolyte choice were assessed to find an appropriate combination for the superheated slurry cast 7075 Al alloy substrate.The alloy was anodized in sulfuric acid electrolyte or alternatively in sulfuric acid mixed with boric acid or citric acid. The voltages applied were in the range of 15-30 V. Anodizing current densities tested were 2 and 3 A/dm^2,while temperatures tested were 5 and 15 ℃. Thickness, surface morphology, hardness,and corrosion resistance of the oxide film were then evaluated.It was found that 25 V,2 A/dm^2 and 5 ℃ were suitable for this alloy when anodized in sulfuric acid. The oxide film was smooth with uniform thickness, low porosity, high hardness,and had the highest corrosion resistance at these parameters. However, discontinuous oxide films were observed from samples anodized at higher temperature of 15 ℃.Alternative electrolytes considered were sulfuric acid mixed with boric acid or citric acid. The results showed that electrolytes with boric acid or citric acid increased thickness, hardness, corrosion resistance and quality of the oxide films.However, these oxide films were inferior to those obtained with sulfuric acid electrolyte at lower temperature(25 V, 2 A/dm^2 and5 ℃).展开更多
基金Project(HEUFT05038)supported by the Basic Research Foundation of Harbin Engineering University,ChinaProject(2009AA03Z423)supported by the National High-Tech Research and Development Program of China
文摘The effects of isothermal holding time on the semisolid microstructure of Mg-9Al-1Si(mass fraction,%)alloy were investigated.The research results indicate that the Mg-9Al-1Si alloy with non-dendritic microstructure can be produced by the semi-solid isothermal heat treatment.With holding time varying from 5 to 30 min,the volume fraction of liquid is gradually enlarged from 29.3%to 38.6%,the morphology ofα-Mg grains changes from initial dendritic shape to spherical types and their average sizes increases from 41.1 to 56.1μm.In addition,during the isothermal heat treatment,the eutectic Mg2Si phase changes from the initial Chinese script shape to granule and/or polygon shape in Mg-9Al-1Si alloy.The modification of Mg2Si phase is possibly attributed to a shift of the eutectic composition of the liquid in semi-solid slurries,towards lower silicon contents with increasing Al content due to a redistribution of Al during isothermal heat treatment.
基金Sponsored by the Natural Science Foundation of Heilongjiang Province (Grant No.E2004-06)
文摘Microengines are regarded as the potential replacements for batteries.Aimed at the unsatisfactory thermal property of silicon used in the combustion chambers,ceramics are chosen as the construction material in this paper.The fabrication process where alumina has been chosen as the microengine material is discussed.Vigorous FEA has been carried out,and it is found that the material satisfies the stress and deformation requirements of the design.Then the alumina fabrication process is described.Soft reusable polydimethylsiloxane(PDMS)moulds are produced from SU-8 resist masters,and alumina microengine parts are produced using the PDMS moulds.Images of the ceramic components show that the fabrication satisfies the design requirements.
基金financially supported by the Higher Education Research Promotionthe National Research University Project of Thailand, Office of the Higher Education (Contract No. ENG580529S)+2 种基金Center of Excellence in Materials Engineering (CEME)the Graduate Engineer Scholarship and the Graduate School ScholarshipPrince of Songkla University, including Surat Thani Campus (2016)
文摘The anodizing parameters of voltage, current density, temperature, and electrolyte choice were assessed to find an appropriate combination for the superheated slurry cast 7075 Al alloy substrate.The alloy was anodized in sulfuric acid electrolyte or alternatively in sulfuric acid mixed with boric acid or citric acid. The voltages applied were in the range of 15-30 V. Anodizing current densities tested were 2 and 3 A/dm^2,while temperatures tested were 5 and 15 ℃. Thickness, surface morphology, hardness,and corrosion resistance of the oxide film were then evaluated.It was found that 25 V,2 A/dm^2 and 5 ℃ were suitable for this alloy when anodized in sulfuric acid. The oxide film was smooth with uniform thickness, low porosity, high hardness,and had the highest corrosion resistance at these parameters. However, discontinuous oxide films were observed from samples anodized at higher temperature of 15 ℃.Alternative electrolytes considered were sulfuric acid mixed with boric acid or citric acid. The results showed that electrolytes with boric acid or citric acid increased thickness, hardness, corrosion resistance and quality of the oxide films.However, these oxide films were inferior to those obtained with sulfuric acid electrolyte at lower temperature(25 V, 2 A/dm^2 and5 ℃).
