The Mg-3.0Nd-0.2Zn-0.4Zr (NZ30K) alloys were prepared by direct-chill casting (DCC) and sand mould casting (SMC) processes,respectively and their microstructures and mechanical properties were investigated.The results...The Mg-3.0Nd-0.2Zn-0.4Zr (NZ30K) alloys were prepared by direct-chill casting (DCC) and sand mould casting (SMC) processes,respectively and their microstructures and mechanical properties were investigated.The results indicate that casting method plays a remarkable influence on the microstructure and mechanical properties of as-cast NZ30K alloy.The grain size increases from 35-40μm in the billets made by the DCC to about 100-120μm in the billets by the SMC.The aggregation of Mg12Nd usually found at the triple joints of grain boundaries in the billets prepared by SMC while is not observable from the billets by DCC.The tensile strengths and elongations of the billets are 195.2 MPa and 15.5% by DCC,and 162.5 MPa and 3.2% by SMC,respectively.The tensile strength of the alloy by DCC is remarkably enhanced by T6 heat treatment,which reached 308.5 MPa.Fracture surfaces of NZ30K alloy have been characterized as intergranular fracture by SMC and quasi-cleavage fracture by DCC,respectively.展开更多
As most Mg alloy products are now produced by a casting process,the development of high strength cast Mg alloys can promote their further applications and has already become one of the hot research areas of Mg alloys....As most Mg alloy products are now produced by a casting process,the development of high strength cast Mg alloys can promote their further applications and has already become one of the hot research areas of Mg alloys.The present paper reviews the strengthening mechanisms,tensile properties and modification results of commercial high strength cast Mg alloys;as well as the development of Mg-Gd,Mg-Nd and Mg-Sn based alloys.It concludes that precipitation strengthening is the most important strengthening mechanism in high strength cast Mg alloys,which contributes more than 60%of yield strength in solution&peak-aged(T6)cast Mg alloys.For the yield strength,the alloys follow the sequence of Mg-Gd(Y)-Ag>Mg-Gd(Y)-Zn>Mg-Gd-Y/Sm/Nd>Mg-Y-Nd(WE series)>ZK61>Mg-Nd>AZ91>Mg-Sn.Mg-Gd(Y)-Ag based alloys are the strongest cast Mg alloys at present,followed by Mg-Gd(Y)-Zn based alloys.The high yield strengths of Mg-Gd(Y)-Ag and Mg-Gd(Y)-Zn cast alloys are due to the co-precipitation of basal and prismatic meta-stable phases.展开更多
The microstructure and mechanical properties of Mg-Zn-Ho-Zr alloys have been investigated in detail. The grain size of the as-cast Mg-Zn-Ho-Zr alloy was greatly decreased by the addition of Ho, and the grain growth du...The microstructure and mechanical properties of Mg-Zn-Ho-Zr alloys have been investigated in detail. The grain size of the as-cast Mg-Zn-Ho-Zr alloy was greatly decreased by the addition of Ho, and the grain growth during solution treatment was suppressed by Mg-Zn-Ho phases formed at grain boundaries. These thermally stable Mg-Zn-Ho phases could not completely dissolve into the matrix dur- ing solution treatment, and the strengthening effect of solution-plus-ageing treatment weakened. The addition of Ho can greatly enhance the high-temperature elongation of the Mg-Zn-Ho-Zr alloy, but the increase of high-temperature tensile strength was just a little.展开更多
The differences of the microstructure and mechanical property between metal mould and sand mould cast Mg-10Gd-3Y-Zr alloy were investigated both under as-cast condition and after solution heat treatment.In the as-cast...The differences of the microstructure and mechanical property between metal mould and sand mould cast Mg-10Gd-3Y-Zr alloy were investigated both under as-cast condition and after solution heat treatment.In the as-cast specimens,the microstructure is similar and composed of α-Mg solid solution and eutectic compound of α-Mg+ Mg24(Gd,Y) 5;whereas the grain size using metal mould and sand mould is 27 μm and 71 μm,respectively.The eutectic compound of metal mould cast alloy was completely dissolved after solution treated at 500℃ for 8 h,however it needs higher temperature(525 ℃) and longer time(12 h) to achieve the absolute dissolving under sand mould condition.In contrast to metal mould,the peak time of sand mould alloy aged at 225 ℃ and 250 ℃ of was advanced by 4 h and 6 h,respectively.The precipitation reaction sequence in sand mould cast Mg-10Gd-3Y-Zr alloy during isothermal ageing at 250 ℃ follows S.S.S.S.→β″(D019) →β'(cboc) →β1(fcc) →β(fcc) ,which is similar to that in the alloy cast using metal mould.展开更多
The new magnesium-alloy fluxes are developed. composed of some chlorides and nuorides of alkalimetals and a few other inorganic substances,these fluxes show a very good comprehensive performance in relation to the mel...The new magnesium-alloy fluxes are developed. composed of some chlorides and nuorides of alkalimetals and a few other inorganic substances,these fluxes show a very good comprehensive performance in relation to the melting point,density,viscosity,slag forming capacity and so on. Compared with the traditional fluxes,these new fluxes have better spreading performance,longer holding capacity,better parting ability with themelt,lower discharging amount of harmful gases. The five-year’s application has demonstrated that they can effectively keep the Mg-alloy melt from oxidization,improve its metallurgical quality,and have great significancein the environment protection.展开更多
The present investigation studied the effects of different kinds of ceramic foam filters (CFF) incorporating gas bubbling on the microstructure and mechanical properties of virgin AZ91 alloys, and the reactions betwee...The present investigation studied the effects of different kinds of ceramic foam filters (CFF) incorporating gas bubbling on the microstructure and mechanical properties of virgin AZ91 alloys, and the reactions between filters and Mg melt during filtration. The results show that the purification process of CFF incorporating gas bubbling process can obviously improve the R m and A of AZ91 alloy, especially the A. Amongst the selected four kinds of CFF, the MgO filter is the most suitable for filtrating Mg melt, and the filtration effective sequence of four kinds of filtrating materials is as follows: MgO>Al2O3>ZrO2>SiC. With MgO filter incorporating gas bubbling treatment under Ar flow rate of 2 L/min and temperature of 730 °C, the ultimate tensile strength R m and elongation A can be improved greatly from 175.3 MPa and 2.74% to 195.4 MPa and 4.54%, respectively. No inclusions are found on the fracture surface of the sample filtrated by MgO ceramic foam filter, and the fracture mode is quasicleavage crack.展开更多
基金supported by the National High-tech R&D Program of China (863 Program),grant No.2009AA03Z521the foundation of Shanghai Rising-Star Program (A type),grant No. 09QA1403100
文摘The Mg-3.0Nd-0.2Zn-0.4Zr (NZ30K) alloys were prepared by direct-chill casting (DCC) and sand mould casting (SMC) processes,respectively and their microstructures and mechanical properties were investigated.The results indicate that casting method plays a remarkable influence on the microstructure and mechanical properties of as-cast NZ30K alloy.The grain size increases from 35-40μm in the billets made by the DCC to about 100-120μm in the billets by the SMC.The aggregation of Mg12Nd usually found at the triple joints of grain boundaries in the billets prepared by SMC while is not observable from the billets by DCC.The tensile strengths and elongations of the billets are 195.2 MPa and 15.5% by DCC,and 162.5 MPa and 3.2% by SMC,respectively.The tensile strength of the alloy by DCC is remarkably enhanced by T6 heat treatment,which reached 308.5 MPa.Fracture surfaces of NZ30K alloy have been characterized as intergranular fracture by SMC and quasi-cleavage fracture by DCC,respectively.
基金supported by the National Natural Science Foundation of China(51201103&51304135)the Specialized Research Fund for the Doctoral Program of Higher Education(20110073120008)+2 种基金the New Century Excellent Talents in University of Ministry of Education of China(NCET-11-0329)the Program of Shanghai Subject Chief of Engineering(14XD1425000)the Assembly Pre-research Project(51312030706)
文摘As most Mg alloy products are now produced by a casting process,the development of high strength cast Mg alloys can promote their further applications and has already become one of the hot research areas of Mg alloys.The present paper reviews the strengthening mechanisms,tensile properties and modification results of commercial high strength cast Mg alloys;as well as the development of Mg-Gd,Mg-Nd and Mg-Sn based alloys.It concludes that precipitation strengthening is the most important strengthening mechanism in high strength cast Mg alloys,which contributes more than 60%of yield strength in solution&peak-aged(T6)cast Mg alloys.For the yield strength,the alloys follow the sequence of Mg-Gd(Y)-Ag>Mg-Gd(Y)-Zn>Mg-Gd-Y/Sm/Nd>Mg-Y-Nd(WE series)>ZK61>Mg-Nd>AZ91>Mg-Sn.Mg-Gd(Y)-Ag based alloys are the strongest cast Mg alloys at present,followed by Mg-Gd(Y)-Zn based alloys.The high yield strengths of Mg-Gd(Y)-Ag and Mg-Gd(Y)-Zn cast alloys are due to the co-precipitation of basal and prismatic meta-stable phases.
基金supported by the National Natural Science Foundation of China (No.51074106)the International Cooperation Fund of Shanghai Science and Technology Committee:Shanghai/Rhone-Alpes Science and Technology Cooperation Fund (No. 06SR07104)+1 种基金the National High-Tech Research and Development Program of China (No.2009AA033501)the National High-Tech Research and Development Program of China (No.2006BAE04B01-2)
文摘The microstructure and mechanical properties of Mg-Zn-Ho-Zr alloys have been investigated in detail. The grain size of the as-cast Mg-Zn-Ho-Zr alloy was greatly decreased by the addition of Ho, and the grain growth during solution treatment was suppressed by Mg-Zn-Ho phases formed at grain boundaries. These thermally stable Mg-Zn-Ho phases could not completely dissolve into the matrix dur- ing solution treatment, and the strengthening effect of solution-plus-ageing treatment weakened. The addition of Ho can greatly enhance the high-temperature elongation of the Mg-Zn-Ho-Zr alloy, but the increase of high-temperature tensile strength was just a little.
基金funded by the National Basic Research Program of China under contract No.2007CB613701National Key Technology R&D Program of China under contract No.2006BAE04B07-2Program of Shanghai Subject Chief Scientist under contract No.08XD14020
文摘The differences of the microstructure and mechanical property between metal mould and sand mould cast Mg-10Gd-3Y-Zr alloy were investigated both under as-cast condition and after solution heat treatment.In the as-cast specimens,the microstructure is similar and composed of α-Mg solid solution and eutectic compound of α-Mg+ Mg24(Gd,Y) 5;whereas the grain size using metal mould and sand mould is 27 μm and 71 μm,respectively.The eutectic compound of metal mould cast alloy was completely dissolved after solution treated at 500℃ for 8 h,however it needs higher temperature(525 ℃) and longer time(12 h) to achieve the absolute dissolving under sand mould condition.In contrast to metal mould,the peak time of sand mould alloy aged at 225 ℃ and 250 ℃ of was advanced by 4 h and 6 h,respectively.The precipitation reaction sequence in sand mould cast Mg-10Gd-3Y-Zr alloy during isothermal ageing at 250 ℃ follows S.S.S.S.→β″(D019) →β'(cboc) →β1(fcc) →β(fcc) ,which is similar to that in the alloy cast using metal mould.
文摘The new magnesium-alloy fluxes are developed. composed of some chlorides and nuorides of alkalimetals and a few other inorganic substances,these fluxes show a very good comprehensive performance in relation to the melting point,density,viscosity,slag forming capacity and so on. Compared with the traditional fluxes,these new fluxes have better spreading performance,longer holding capacity,better parting ability with themelt,lower discharging amount of harmful gases. The five-year’s application has demonstrated that they can effectively keep the Mg-alloy melt from oxidization,improve its metallurgical quality,and have great significancein the environment protection.
基金supported by Program of Shanghai Subject Chief Scientist (No.08XD14020)National Basic Research Program of China (No.2007CB613701)+1 种基金National High Technology R&D Program of China (No.2009AA033501)Aerospace Science and Technology Innovation Fund of China Aerospace Science and Technology Corporation (No.0502)
文摘The present investigation studied the effects of different kinds of ceramic foam filters (CFF) incorporating gas bubbling on the microstructure and mechanical properties of virgin AZ91 alloys, and the reactions between filters and Mg melt during filtration. The results show that the purification process of CFF incorporating gas bubbling process can obviously improve the R m and A of AZ91 alloy, especially the A. Amongst the selected four kinds of CFF, the MgO filter is the most suitable for filtrating Mg melt, and the filtration effective sequence of four kinds of filtrating materials is as follows: MgO>Al2O3>ZrO2>SiC. With MgO filter incorporating gas bubbling treatment under Ar flow rate of 2 L/min and temperature of 730 °C, the ultimate tensile strength R m and elongation A can be improved greatly from 175.3 MPa and 2.74% to 195.4 MPa and 4.54%, respectively. No inclusions are found on the fracture surface of the sample filtrated by MgO ceramic foam filter, and the fracture mode is quasicleavage crack.
