In this study,the effect of rotating gas bubble stirring treatment on the microstructures of semi-solid AZ91-2Ca alloy was investigated.The semi-solid slurry was produced by injecting fine gas bubbles into the melt th...In this study,the effect of rotating gas bubble stirring treatment on the microstructures of semi-solid AZ91-2Ca alloy was investigated.The semi-solid slurry was produced by injecting fine gas bubbles into the melt through a rotating steel diffuser during solidification,and the samples of semi-solid slurry were taken by the rapid quenching method.The results show that fine and sphericalα-Mg particles can be obtained under rotating gas bubble stirring treatment.The process parameters such as gas flow rate,cooling rate and rotation speed have significant influence on the morphology of primary solid particles.After rotating gas bubble stirring treatment,the higher the particle density,the finer and rounder the primaryα-Mg particles.The formation of numerous solid particles is due to the combination mechanisms of copious nucleation and dendrite fragmentation.展开更多
To improve the corrosion resistance of wrought magnesium alloys through rare earth (RE) additions, the corrosion behaviour of Mg-5Zn-0.3Zr-xNd (x=0, 1, and 2; wt%) and Mg-5Zn-0.3Zr-2Nd-yY (y=0.5 and 1; wt%) allo...To improve the corrosion resistance of wrought magnesium alloys through rare earth (RE) additions, the corrosion behaviour of Mg-5Zn-0.3Zr-xNd (x=0, 1, and 2; wt%) and Mg-5Zn-0.3Zr-2Nd-yY (y=0.5 and 1; wt%) alloys in a 5wt% NaCl solution was investigated using immersion test and electrochemical measurements. The results of immersion test show that Mg-5Zn-0.3Zr-2Nd alloy exhibits the best corrosion resistance among the tested alloys. Electrochemical measurements show that secondary phases in RE-containing Mg-5Zn-0.3Zr alloys behave as less noble cathodes in micro-galvanic corrosion and suppress the cathodic process. The additions of Nd and Y into Mg-5Zn-0.3Zr alloy also improve the compactness of the corrosion product film and are beneficial to the corrosion resistance.展开更多
The corrosion behaviors of low-pressure sand cast Mg-10Gd-3Y-0.5Zr(wt.%) alloys in as-cast, solution treated(T4) and aged(T6) conditions were studied by means of immersion test and electrochemical measurements in 5wt....The corrosion behaviors of low-pressure sand cast Mg-10Gd-3Y-0.5Zr(wt.%) alloys in as-cast, solution treated(T4) and aged(T6) conditions were studied by means of immersion test and electrochemical measurements in 5wt.% NaCl solution saturated with Mg(OH)_2. It was observed that the corrosion rate in the T4 condition was lower than that of the as-cast and T6 conditions by both sand casting and permanent mold casting with the same order of as-cast>T6>T4; while the corrosion resistance of the permanent mold casting is superior to the sand casting. The morphologies of the corrosion products are similar porous structures consisting of tiny erect flakes perpendicular to the corroded surface of the alloy, irrespective of the heat treatment conditions. Especially, the corrosion film in T4 condition is more compact than that in the other two conditions. In addition, the severer corrosion happening to the as-cast condition is correlated with the galvanic corrosion between the matrix and the eutectic compounds; while improved corrosion resistance for the T4 and T6 conditions is ascribed to the dissolution of the secondary eutectic compounds. The measured corrosion current densities of Mg-10Gd-3Y-0.5Zr alloys in as-cast, T4, and T6 conditions are 36 μA?cm^(-2), 10 μA?cm^(-2), and 33 μA?cm^(-2), respectively. The proposed equivalent circuit [Rs(CPE_1(R_t(R_fCPE_2))] by Zview software matches well with the tested electrochemical impedance spectra(EIS) data.展开更多
Progressive solidification is usually considered an effective strategy to reduce the hot tearing susceptibility of a cast component.In this study,special constrained plate castings with progressive changes in cross-se...Progressive solidification is usually considered an effective strategy to reduce the hot tearing susceptibility of a cast component.In this study,special constrained plate castings with progressive changes in cross-section were designed,which enabled progressive solidification.The hot tearing behavior of a newly developed NZ30 K Mg alloy(Mg-3.0 Nd-0.2 Zn-Zr,wt.%)was studied under progressive solidification using various mold temperature distributions and constraint lengths.Of these,a homogeneous mold temperature distribution is found to be the best option to avoid hot tearing,followed by a local low mold temperature distribution(with a chiller),then a gradient mold temperature distribution.Unexpectedly,compared with the homogeneous mold temperature distribution,adding a chiller does not provide any further reduction in the hot tearing susceptibility of the NZ30 K Mg alloy.A high mold temperature and a short constraint length increase the hot tearing resistance of cast Mg alloys.Progressive solidification is not a sufficient and necessary condition to avoid the formation of hot tearing.The two key factors that determine the occurrence of hot tearing under progressive solidification are the maximum cooling rate and the constraint length.Decreasing these values can reduce the incidence of hot tearing.展开更多
First-principles calculations within generalized gradient approximation have been performed to investigate ideal strengths of anti-fluorite structured Mg_(2)X(X¼Si,Ge,Sn and Pb)compounds.The present calculations ...First-principles calculations within generalized gradient approximation have been performed to investigate ideal strengths of anti-fluorite structured Mg_(2)X(X¼Si,Ge,Sn and Pb)compounds.The present calculations showed that the ideal tensile strengths of Mg_(2)X occur in the[111]directions while the ideal shear strengths appear in the(111)[11-2]systems.Both ideal tensile strength and shear strength of Mg_(2)X(X¼Si,Ge,Sn and Pb)decreased gradually with the increase of atomic number of X.The microscopic process and inherent mechanisms of mechanical properties were discussed from the evolution of electronic structures during strain.展开更多
This study investigates the eff ect of solution treatment(at 470°C for 0–48 h)on the microstructural evolution,tensile properties,and impact properties of an Al–5.0Mg–3.0Zn–1.0Cu(wt%)alloy prepared by permane...This study investigates the eff ect of solution treatment(at 470°C for 0–48 h)on the microstructural evolution,tensile properties,and impact properties of an Al–5.0Mg–3.0Zn–1.0Cu(wt%)alloy prepared by permanent gravity casting.The results show that the as-cast microstructure consists ofα-Al dendrites and a network-like pattern of T-Mg32(AlZnCu)49 phases.Most of the T-phases were dissolved within 24 h at 470℃;and a further prolonging of solution time resulted in a rapid growth ofα-Al grains.No transformation from the T-phase to the S-Al2CuMg phase was discovered in this alloy.Both the tensile properties and impact toughness increased quickly,reached a maximum peak value,and decreased gradually as the solution treatment proceeded.The impact toughness is more closely related to the elongation,and the relationship between impact toughness and elongation appears to obey an equation:IT=8.43 EL-3.46.After optimal solution treatment at 470℃for 24 h,this alloy exhibits excellent mechanical properties with the ultimate tensile strength,yield strength,elongation and impact toughness being 431.6 MPa,270.1 MPa,19.4%and 154.7 kJ/m^(2),which are comparable to that of a wrought Al–6.0 Mg–0.7 Mn alloy(5E06,a 5 xxx aluminum alloy).Due to its excellent comprehensive combination of mechanical properties,this cast alloy has high potential for use in components which require medium strength,high ductility and high toughness.展开更多
This study examines the relationship among cooling rate,microstructure and mechanical properties of a sand-casted Al-5.0 Mg-0.6 Mn-0.25 Ce(wt%)alloy subjected to T4 heat treatment(430℃×12 h+natural aging for 5 d...This study examines the relationship among cooling rate,microstructure and mechanical properties of a sand-casted Al-5.0 Mg-0.6 Mn-0.25 Ce(wt%)alloy subjected to T4 heat treatment(430℃×12 h+natural aging for 5 days),and the tested alloys with wall thickness varying from 5 to 50 mm were prepared.The results show that as the cooling rate increases from0.22 to 7.65 K/s,the average secondary dendritic arm spacing(SDAS,λ2)decreases from 94.8 to 27.3μm.The relation between SDAS and cooling rate can be expressed by an equation:λ2=53.0 Rc-0345.Additionally,an increase in cooling rate was shown not only to reduce the amount of the secondary phases,but also to promote the transition from Al10 Mn2 Ce toα-Al24(Mn,Fe)6Si2 phase.Tensile tests show that as the cooling rate increases from 0.22 to 7.65 K/s,the ultimate tensile strength(UTS)increases from 146.3 to 241.0 MPa and the elongation(EL)increases sharply from 4.4 to 12.2%for the ascast alloys.Relations of UTS and EL with SDAS were determined,and both the UTS and EL increase linearly with(1/λ2)0.5and that these changes can be explained by strengthening mechanisms.Most eutectic Al3Mg2 phases were dissolved during T4 treatment,which in turn further improve the YS,UTS and EL.However,the increment percent of YS,UTS and EL is affected by the cooling rate.展开更多
基金supported by the National Key Research and Development Program of China(No.2021YFB3501002)the National Science and Technology Major Project of China(No.J2019-Ⅷ-0003-0165)Qinghai Salt Lake Industry Co.,Ltd.financially by the Science and Technology Project,China(No.21-ZC0609-0003)。
基金This work was financially supported by the National Natural Science Foundation of China(No.U1804251)the Shanghai Municipal Commission of Economy and Information,China(No.GYQJ-2019-1-27)+2 种基金the Science and Technology Commission of Shanghai Municipality,China(Nos.18441908000,19441906300,19441913400)the Shenzhen’s Three Renowned Project,China(No.SZSM201612092)the Shanghai Jiao Tong University Medical-engineering Cross Fund,China(No.YG2019ZDA02).
基金This project is sponsored by National Natural Science Foundation of China(No.51275295)Funded Projects of SAST-SJTU Joint Research Centre of Advanced Aerospace Technology(No.USCAST2012-15)Research Fund for the Doctoral Program of Higher Education of China(No.20120073120011).
文摘In this study,the effect of rotating gas bubble stirring treatment on the microstructures of semi-solid AZ91-2Ca alloy was investigated.The semi-solid slurry was produced by injecting fine gas bubbles into the melt through a rotating steel diffuser during solidification,and the samples of semi-solid slurry were taken by the rapid quenching method.The results show that fine and sphericalα-Mg particles can be obtained under rotating gas bubble stirring treatment.The process parameters such as gas flow rate,cooling rate and rotation speed have significant influence on the morphology of primary solid particles.After rotating gas bubble stirring treatment,the higher the particle density,the finer and rounder the primaryα-Mg particles.The formation of numerous solid particles is due to the combination mechanisms of copious nucleation and dendrite fragmentation.
基金supported by the Program of Shanghai Subject Chief Scientist (No.08XD14020)the Science and Technology Commission of Shanghai Municipality (No.08JC1412200)China Postdoctoral Science Foundation (No.20080430657)
文摘To improve the corrosion resistance of wrought magnesium alloys through rare earth (RE) additions, the corrosion behaviour of Mg-5Zn-0.3Zr-xNd (x=0, 1, and 2; wt%) and Mg-5Zn-0.3Zr-2Nd-yY (y=0.5 and 1; wt%) alloys in a 5wt% NaCl solution was investigated using immersion test and electrochemical measurements. The results of immersion test show that Mg-5Zn-0.3Zr-2Nd alloy exhibits the best corrosion resistance among the tested alloys. Electrochemical measurements show that secondary phases in RE-containing Mg-5Zn-0.3Zr alloys behave as less noble cathodes in micro-galvanic corrosion and suppress the cathodic process. The additions of Nd and Y into Mg-5Zn-0.3Zr alloy also improve the compactness of the corrosion product film and are beneficial to the corrosion resistance.
基金sponsored by the National Natural Science Foundation of China(No.51275295)Research Fund for the Doctoral Program of Higher Education of China(Nos.20120073120011 and 20130073110052)
文摘The corrosion behaviors of low-pressure sand cast Mg-10Gd-3Y-0.5Zr(wt.%) alloys in as-cast, solution treated(T4) and aged(T6) conditions were studied by means of immersion test and electrochemical measurements in 5wt.% NaCl solution saturated with Mg(OH)_2. It was observed that the corrosion rate in the T4 condition was lower than that of the as-cast and T6 conditions by both sand casting and permanent mold casting with the same order of as-cast>T6>T4; while the corrosion resistance of the permanent mold casting is superior to the sand casting. The morphologies of the corrosion products are similar porous structures consisting of tiny erect flakes perpendicular to the corroded surface of the alloy, irrespective of the heat treatment conditions. Especially, the corrosion film in T4 condition is more compact than that in the other two conditions. In addition, the severer corrosion happening to the as-cast condition is correlated with the galvanic corrosion between the matrix and the eutectic compounds; while improved corrosion resistance for the T4 and T6 conditions is ascribed to the dissolution of the secondary eutectic compounds. The measured corrosion current densities of Mg-10Gd-3Y-0.5Zr alloys in as-cast, T4, and T6 conditions are 36 μA?cm^(-2), 10 μA?cm^(-2), and 33 μA?cm^(-2), respectively. The proposed equivalent circuit [Rs(CPE_1(R_t(R_fCPE_2))] by Zview software matches well with the tested electrochemical impedance spectra(EIS) data.
基金supported by the National Key Research and Development Program of China(Grant Nos.:2016YFB0701204 and 2016YFB0301002)the National Natural Science Foundation of China(Grant Nos.:51671128,51771113,and 51821001)the Shanghai Rising-Star Program(Grant No.:15QB1402700)。
文摘Progressive solidification is usually considered an effective strategy to reduce the hot tearing susceptibility of a cast component.In this study,special constrained plate castings with progressive changes in cross-section were designed,which enabled progressive solidification.The hot tearing behavior of a newly developed NZ30 K Mg alloy(Mg-3.0 Nd-0.2 Zn-Zr,wt.%)was studied under progressive solidification using various mold temperature distributions and constraint lengths.Of these,a homogeneous mold temperature distribution is found to be the best option to avoid hot tearing,followed by a local low mold temperature distribution(with a chiller),then a gradient mold temperature distribution.Unexpectedly,compared with the homogeneous mold temperature distribution,adding a chiller does not provide any further reduction in the hot tearing susceptibility of the NZ30 K Mg alloy.A high mold temperature and a short constraint length increase the hot tearing resistance of cast Mg alloys.Progressive solidification is not a sufficient and necessary condition to avoid the formation of hot tearing.The two key factors that determine the occurrence of hot tearing under progressive solidification are the maximum cooling rate and the constraint length.Decreasing these values can reduce the incidence of hot tearing.
基金This work is supported by Natural Science Foundation of China(51071053)of Guangxi Province(0991051)+2 种基金also Key Laboratory of Materials Design and Preparation Technology of Hunan Province(KF0803)the Hunan Provincial Innovation Foundation for Graduate(No.CX2012B244)the Scientific Research Foundation of Guangxi University(X071117).
文摘First-principles calculations within generalized gradient approximation have been performed to investigate ideal strengths of anti-fluorite structured Mg_(2)X(X¼Si,Ge,Sn and Pb)compounds.The present calculations showed that the ideal tensile strengths of Mg_(2)X occur in the[111]directions while the ideal shear strengths appear in the(111)[11-2]systems.Both ideal tensile strength and shear strength of Mg_(2)X(X¼Si,Ge,Sn and Pb)decreased gradually with the increase of atomic number of X.The microscopic process and inherent mechanisms of mechanical properties were discussed from the evolution of electronic structures during strain.
基金the United Fund of National Natural Science Foundation of China and Yunnan Province(No.U1902220)the National Natural Science Foundation of China(No.51674166)。
文摘This study investigates the eff ect of solution treatment(at 470°C for 0–48 h)on the microstructural evolution,tensile properties,and impact properties of an Al–5.0Mg–3.0Zn–1.0Cu(wt%)alloy prepared by permanent gravity casting.The results show that the as-cast microstructure consists ofα-Al dendrites and a network-like pattern of T-Mg32(AlZnCu)49 phases.Most of the T-phases were dissolved within 24 h at 470℃;and a further prolonging of solution time resulted in a rapid growth ofα-Al grains.No transformation from the T-phase to the S-Al2CuMg phase was discovered in this alloy.Both the tensile properties and impact toughness increased quickly,reached a maximum peak value,and decreased gradually as the solution treatment proceeded.The impact toughness is more closely related to the elongation,and the relationship between impact toughness and elongation appears to obey an equation:IT=8.43 EL-3.46.After optimal solution treatment at 470℃for 24 h,this alloy exhibits excellent mechanical properties with the ultimate tensile strength,yield strength,elongation and impact toughness being 431.6 MPa,270.1 MPa,19.4%and 154.7 kJ/m^(2),which are comparable to that of a wrought Al–6.0 Mg–0.7 Mn alloy(5E06,a 5 xxx aluminum alloy).Due to its excellent comprehensive combination of mechanical properties,this cast alloy has high potential for use in components which require medium strength,high ductility and high toughness.
基金supported financially by the National Natural Science Foundation of China (No.51674166)
文摘This study examines the relationship among cooling rate,microstructure and mechanical properties of a sand-casted Al-5.0 Mg-0.6 Mn-0.25 Ce(wt%)alloy subjected to T4 heat treatment(430℃×12 h+natural aging for 5 days),and the tested alloys with wall thickness varying from 5 to 50 mm were prepared.The results show that as the cooling rate increases from0.22 to 7.65 K/s,the average secondary dendritic arm spacing(SDAS,λ2)decreases from 94.8 to 27.3μm.The relation between SDAS and cooling rate can be expressed by an equation:λ2=53.0 Rc-0345.Additionally,an increase in cooling rate was shown not only to reduce the amount of the secondary phases,but also to promote the transition from Al10 Mn2 Ce toα-Al24(Mn,Fe)6Si2 phase.Tensile tests show that as the cooling rate increases from 0.22 to 7.65 K/s,the ultimate tensile strength(UTS)increases from 146.3 to 241.0 MPa and the elongation(EL)increases sharply from 4.4 to 12.2%for the ascast alloys.Relations of UTS and EL with SDAS were determined,and both the UTS and EL increase linearly with(1/λ2)0.5and that these changes can be explained by strengthening mechanisms.Most eutectic Al3Mg2 phases were dissolved during T4 treatment,which in turn further improve the YS,UTS and EL.However,the increment percent of YS,UTS and EL is affected by the cooling rate.