Effect of Lanthanum-praseodymium-cerium Mischmetal on Mechanical Properties and Microstructure of Mg-A1 Alloys

The effects of lanthanum-praseodymium-cerium mischmetal (LPC) on the microstructure and mechanical properties of Mg-Al alloy were investigated. With the addition of LPC, an additional rod-like Al11La3 phase was deposited in the alloy. LPC greatly improves the tensile strength of cast Mg-Al alloys but negatively affects the elongation of cast alloys above 473 K. Cast alloys are strengthened by both precipitation strengthening and dispersion strengthening at ambient temperature. When the temperature exceeds 4...     

Preparation of Plate Fe60 Co8 Zr10 Mo5 W2 B15 Bulk Amorphous Alloy and Its Fracture Toughness

With processes of arc melting, inductive melting and copper mold suction casting, a plate Febased bulk amorphous alloy Fe₆₀Co₈Zr₁₀Mo₅W₂B₁₅ with a thickness of 1 mm was prepared. The surfaces and fractures of the cast bulk amorphous alloy were aglean and with typical metallic luster. The glass transition temperature (T_g), supercooled liquid region (δT_x) and reduced glass transition temperature (T_g) of prepared Fe-based amorphous alloy are 884 K, 63 K, and 0.611 respectively. The fracture toughness of the cast bulk amorphous alloy is at the level of 1.6 MPa·m^1/2. Funded by the Key Project of National Natural Science Foundation of China (No. 50431030) and the Natural Science Foundation of Jiangsu Province (No. BK2001053)     

Preparation and properties of FeZrB amorphous-nanocrystalline soft magnetic alloy

Fe₆₈Zr₂₀B₁₂ amorphous alloy was prepared by mechanical alloying(MA) method and annealed at different temperatures. Microstructures and magnetic properties of Fe₆₈Zr₂₀B₁₂ alloys as-milled and annealed at 693, 843, 943 and 993 K were studied. The raw powders(Fe, Zr, B) formed b. c. c. α-Fe solid solution at early stages of MA and then transformed into amorphous alloy. Grain size(D) of Fe₆₈Zr₂₀B₁₂ alloys increases with increasing annealing temperature and keeps at nanometer level. The specific saturation magnetization(σ _s ) increases with increasing annealing temperature from 300 K to 943 K, and then decreases with annealing temperature at 993 K because of the precipitation of Fe₃B.     

Microstructural characterizations and mechanical properties of Mg-8Sn-1Al-1Zn-xCu alloys

Microstructural characterization and mechanical properties of as-cast Mg-8Sn-1Al-1Zn-xCu（x=0wt%, 1wt%, 1.5wt% and 2.0wt%） alloys were studied by OM, Pandat software, XRD, SEM, DSC and a standard universal testing machine. The experimental results indicate that adding Cu to TAZ811 alloy leads to the formation of the AlMgCu and Cu3 Sn phases. Tensile tests indicate that yield strength increases fi rstly and then decreases with increasing Cu content. The alloy with the addition of 1.5wt% Cu exhibits optimal mechanical properties among the studied alloys. The improved mechanical properties can be ascribed to the second phase strengthening and fi ne-grain strengthening mechanisms resulting from the more dispersed second phases and smaller grain size, respectively. The decrease in ultimate tensile strength and elongation of TAZ811-2.0wt% Cu alloy at room temperature is ascribed to the formation of continuous AlMgCu and coarse Mg2 Sn phases in the liquid state.     

Influence of Mg3N2 powder on microstructures and mechanical properties of AZ31 Mg alloy

In order to obtain an effective and reliable grain refiner for Mg-Al alloys, 1% （mass fraction） Mg3N2 was added into AZ31 Mg alloy. The microstructures of the Mg alloys were studied by optical microscopy, scan electron microscopy and X-ray energy dispersive spectroscopy, and the mechanical properties were determined. The results show that adding a small amount of Mg3N2 to AZ31 Mg alloy can refine the grain size from 103 to 58 μm. The ultimate tensile strength and elongation of AZ31 Mg alloy are 174.1MPa and 8.3%, respectively. After the addition of 1% Mg3N2, the ultimate tensile strength and elongation of AZ31 Mg alloy are increased up to 198.7 MPa and 11.8%, respectively. The grain refinement mechanism is that AIN is formed after Mg3N2 is added. Both AIN and Mg phases are of HCP lattice structure, and the disregistry between Mg phases and AIN along （0001）Mg//（0001）AIN is 3.04%, which is very effective for heterogeneous nucleation.     

New Mg<Subscript>2</Subscript>Si based alloy for automobile engine cylinder liner

New Mg₂Si based alloy were prepared by mechanical alloying. Sintering temperature was from 825 to 865K, which indicated that few Mg₂Si were produced at lower temperature while MgO were produced at higher temperature. Microstructure image showed that at sintering temperature of 855K, Mg₂Si were mostly synthesized with the reaction of purity magnesia powder and silicon powder. Hardness and wear tests proved that the new synthetic silicon magnesium alloy had higher hardness and good wear resistance. Under the same testing conditions, it is found that the hardness of the new material is 420.50, and pure magnesium is only 41.65.In the same experiments it is also found that under the same pressure, pure magnesium alloys than silicon wearing capacity of pure magnesium is 2 times as high that of Mg₂Si based alloy. It shows that Mg₂Si based alloy is the ideal material for the wear parts of car engine cylinder liner because of its small density, stable dimension, high hardness and wear-resisting.     

Influence of flux treatment on the glass forming ability of Pd-Si binary alloys

Pd₈₁Si₁₉ amorphous alloys were prepared by combination methods of melt spinning and B₂O₃ flux treatment. A comparison between the ribbons prepared from the fluxed ingots and the non-fluxed ones has been carried out. The result reveals that after fluxing treatment the glass transition temperature of the as-prepared glassy ribbons is reduced while the initial crystallization temperature is enhanced. It results in that the supercooled liquid region (defined as the difference between the initial crystallization temperature and the glass transition temperature) of the glassy alloy treated with fluxing technology has been increased from 31 to 42 K. This shows that fluxing technique can enhance the glass forming ability (GFA) of the binary alloy and improve the thermal stability of supercooled liquid of the glassy alloy.     

Effect of heat treatments on tensile properties and microstructure of 2195 alloy

Effect of various aging treatments on the tensile properties and microstructure of 2195 alloy has been investigated. The experimental results show that promising combination of strength and ductility is achievable under T₈ temper. The lower aging temperature reduces T₁ precipitation on the subgrain or grain boundaries and favors uniform dispersion of T₁ phases in the matrix, resulting in better strength and ductility. Prior deformation before aging has improved tensile strength with a slight decrease in ductility. Pre-aging after prior deformation had little effect on the age-hardening behavior of 2195 alloy. Project supported by the Key Program of the 9th Five-year Plan of China Synopsis of the first author Zheng Ziqiao, professor, born in 1944, major research fields: physical metallurgy of aluminum alloys; functionally gradient materials; self-propagation high temperature synthesis.     

高强高导电铜合金的研究现状

高强高导电铜合金是一类具有优良综合性能的功能材料和结构材料,被广泛应用于电子、机械等领域.系统总结了固溶强化、形变强化、细晶强化、第二相强化和复合强化等基本原理,指出目前获得高强度高导电铜合金的强化方法和制备工艺,介绍了快速凝固、真空混合铸造法、固-液直接反应法、混合合金法、反应喷射成形法(RSD)等技术在高强高导铜合金生产中的应用,同时,阐述了该类合金的研究现状和发展前景.     

Mechanical properties and microstructure of as-cast and extruded Mg-（Ce, Nd）-Zn-Zr alloys

1INTRODUCTION Thebeneficialinfluenceofrareearth(RE)metalsontheambientandelevatedtemperature mechanicalpropertiesofmagnesiumalloyhaslongbeenrecognized[13].Recently,Yttriumisaddedto Magnesiumalloytoimproveitstensilestrength andcreepresistance,andsuchinvestigationsatheat resistantmagnesiumalloyhaveledtothede velopmentofWE43andWE54alloys[4,5].Al thoughsuchalloysexhibitgoodpropertiesupto573Kthroughcastingandextruding,therelativelyhighcostofYttriumrestrictstheapplicationof suchalloys.Otherr…     

Influences of composition and annealing on the martensitic transformation in Ni-Fe-Ga alloys

A series of Ni-Fe-Ga alloys near the prototype Heusler composition (X₂YZ) were prepared through arc-melting suction-casting method. The dependences of the transformation behavior on the alloy composition and annealing treatment were studied in detail by an optical microscope, X-ray diffraction, and differential scanning calorimeters methods. The experimental results show that the martensitic transformation temperatures increase almost linearly with increasing Ni content in all the NiFeGa alloys. Annealing the Ni_55.5Fe₁₈Ga_26.5 alloy at 100?C500 °C for 3 h and at 300 °C for 1?C10 h shifts the martensitic transformation start temperature by almost 20 °C to high temperature. The variations in the martensitic transformation temperatures in these alloys are discussed in terms of structural differences resulting from alloy composition and annealing treatment.     

Mechanical properties and tribological behavior of a cast heat-resisting copper based alloy

Mechanical properties and tribological behavior of a novel cast heat-resisting copper based alloy are investigated. The corresponding properties of a commercial aluminum bronze C95500 (ASTM B30) are compared with the alloy. The results show that the alloy possesses better mechanical properties and tribological behaviors than that of C95500 at elevated temperature. The tensile strength, elongation and hardness at 500℃ are 470MPa, 2.5% and HB220, respectively. The wear rate of the developed alloy at ambient and elevated temperature is about one-sixth and one-fortieth of that of C95500, respectively. The alloy is very suitable for ma-nufacturing heat-resisting and wear-resisting parts. Major strengthening mechanisms for the alloy are solution strengthening and the second phase strengthening.     

Microstructural features and properties of high-hardness and heat-resistant dispersion strengthened copper by reaction milling

The oxide dispersion strengthened copper alloys are attractive due to their excellent combination of thermal and electrical conductivities,high-temperature strength and microstructure stability.To date,the state-of-art to fabrication of them was the internal oxidation (IO) process.In this paper,alumina dispersion strengthened copper (ADSC) powders of nominal composition of Cu-2.5 vol%Al2O3 were produced by reaction milling (RM) process which was an in-situ gas-solid reaction process.The bulk ADSC alloys for electrical and mechanical properties investigation were obtained by sintering and thereafter hot extrusion.After the hot consolidation processes,the fully densified powder compacts can be obtained.The single γ-Al2O3 phase and profile broaden effects are evident in accordance with the results of X-ray diffraction (XRD);the HRB hardness of the ADSC can be as high as 95;the outcomes should be attributed to the pinning effect of nano γ-Al2O3 on dislocations and grain boundaries in the copper matrix.The electrical conductivity of the ADSC alloy is 55%IACS (International Annealing Copper Standard).The room temperature hardness of the hot consolidated material was approximately maintained after annealing for 1 h at 900 ℃ in hydrogen atmosphere.In terms of the above merits,the RM process to fabricating ADSC alloys is a promising method to improve heat resistance,hardness,electrical conductivity and wear resistance properties etc.     

Compositional dependence of thermal and elastic properties of Cu-Ti-Zr-Ni bulk metallic glasses

Starting from the quaternary Cu47Ti34Zr11Ni8 alloy, the compositional dependence of thermal and elastic properties of Cu-Ti-Zr-Ni alloys was systematically investigated. Quaternary Cu-Ti-Zr-Ni alloys can be cast directly from the melt into copper molds to form fully amorphous strips or rods with the thickness of 3-6 mm. The evidence of the amorphous nature of the cast rods was provided by X-ray spectra. The measured glass transition temperature (Tg) and crystallization temperature (Tx) were obtained for the alloys using differential scanning calorimetry (DSC) at the heating rate of 20 K/s. In the results, the differences between the glass temperature and the crystallization tempera-ture (△Tx=Tx-Tg) are measured with values ranging up to 33-55 K. The reduced glass transition temperature (Trg), which is the ratio of the glass temperature to the liquidus temperature (T1), is often used as an indication of the glass-forming ability of metallic alloys. For the present Cu-Ti-Zr-Ni alloys, this ratio is typically in the range of 0.5838-0.5959, characteristic of metallic alloys with good glass-forming ability. The elastic constants for several selected alloys were measured using ultrasonic methods. The values of the elastic shear modulus, bulk modulus, and Poisson's ratio were also given.     

Rapid monotectic solidification under free fall condition

Thesolidificationprocessofmonotecticalloyhasbeenofgreatinterestformanyyears.Onereasonisthatmonotectictransformation,inwhichoneparentliquidphaseL1decomposessimultaneouslyintoonesolidphaseSandanotherliquidphaseL2,playsanimportantroleintheresearchofphaseseparationandcrystalgrowthkinetics[1—5].Anotherreasonisthatmanyapplicationsofmonotecticalloysinindustry,suchasCu-Pb,Al-Pb,Al-Bi,Al-SnandAl-Inareself-lubricatingbearingalloysorhigh-temperaturesuperconductorsiftheyhavehomogeneouslydispersedmic…     

Effect of heat-treatment on the microstructures and mechanical properties of Mg-10Zn-5Al-0.1Sb-xCu magnesium alloy

The effects of the solution and aging treatment on microstructures and mechanical properties of the Mg-10Zn-5Al-0.1Sb-XCu cast magnesium alloys were investigated by brinell hardness measurement, scanning electron microscopy (SEM), energy spectrum analyzing apparatus and X-ray diffraction (XRD). The experimental results show that the strip-like τ-Mg₃₂ (Al, Zn)₄₉ phase is shown at the grain boundaries and Mg₂Cu phase become smaller, even granular after solution treatment at 350 °C for 24 h. By ageing treatment at 180 °C, the ternary strengthening phase (τ phase) precipitates gradually at or around grain boundary. With increasing aging time, the micro-hardness improves obviously and up to the maximum (105.9 HV) at aging time of 36 h. In addition, the tensile-strengths at room temperature and at an elevated temperature respectively reach 228 MPa and 176 MPa, which is increased by 20% and 10%, respectively.     

Formation and mechanical properties of ductile Fe-based amorphous alloys using a cast iron with minor addition of B and Al

Fe-based amorphous alloys with ductility were synthesized using the commercial cast iron QT50 (denoted as QT) with the combining minor addition of B and Al by single roller melt-spinning. The melt-spun (QT_1-xB_x)₉₉Al₁ (x is from 0.006wt% to 0.01wt%) amorphous alloys exhibit onset crystallization temperatures and Curie temperatures of 759–780 and 629–642 K respectively, and which increase with B content. The amorphous ribbons are ductile and can be bent 180° without breaking. With the increase in B content from 0.006wt% to 0.01wt%, the Vickers microhardness of the amorphous alloys increases from Hv 830 to Hv 1110. The effects of the additional B and Al elements on the glass forming ability and mechanical properties were also discussed.     

Influence of Cr2O3-Al2O3 composite oxide scale on oxidation resistance of ZG40Cr24

Test alloys ZG40Cr24 with alloying of 3 wt% aluminium were cast by intermediate frequency induction furnace. The oxidation resistance of test alloys at 1 000 ℃ for 500 hours was examined according to oxidation weight gain method. The scale morphology and composition were studied using scanning electron microscope (SEM) and X-ray diffraction (XRD) respectively. By energy dispersive spectroscopy (EDS) studies, a kind of composite oxide scale compounded highly by Cr2O3, Al2O3 and spinel MCr2O4 in molecule scale came into being at high temperature. With flat and compact structure, fine and even grains, such composite scale granted complete oxidation resistance to alloy ZG40Cr24. The oxidation resistance mechanism was studied deeply in electrochemistry corrosion. The P+N semiconductor composite scale composed plenty of inner PN junctions, of which the unilateral conductive and the out-of-order arrangement endowed itself insulating in all directions. The positive and negative charges in scale could not move, and the mobile number and transferring rate of them both dropped enormously, as a result, the oxidation rate of the matrix metal was cut down greatly. So the composite scale presented excellent oxidation resistance.     

Mg_2Si的声子谱与力热性能的第一性原理计算

针对6xxx系铝合金的主要强化相Mg2Si的力热性能,采用密度泛函理论、第一性原理以及CASTEP软件进行了理论计算,得到了Mg2Si的平衡晶格常数、弹性系数、声子谱、声子态密度以及相关热力学参量,并对计算曲线进行了理论分析.结果表明:合金强化相Mg2Si的刚性较好,脆性较强,在合金中能起到强化作用.通过声子谱及声子态密度曲线可知,存在9条色散关系曲线,其中3条为声学波,6条为光学波,且频率在8.51 THz附近的格波振动较强.随着温度的增加,熵、焓均增加,而自由能减少.当温度低于200 K时,热容量随着温度的增加而明显增加;当温度高于400K后,热容量接近于常量,其计算结果与物理规律一致.     

Solidified morphology and mechanism of bulk nanocrystalline Fe80P13C7 alloy at isothermal undercooling

The molten Fe80P13C7 alloys can achieve a large undercooling up to 320 K by fluxing technique.With the help of fluxing technique,the molten Fe80P13C7 alloys can be solidified at different undercooling(△T)through isothermal undercooling experiment.It is indicated that the microstructure of the solidified Fe80P13C7 alloy specimens is refined significantly with the increasing undercooling and the grain size is about 20μm,10μm,200 nm and 70 nm for△T=50 K,150 K,250 K and 320 K,respectively.The solidification morphologies of the solidified Fe80P13C7 alloy specimens under different undercooling are quite different.When△T=50 K,it presents a traditional solidification microstructure under a undercooling condition,composed of the primary dendrite and anomalous eutectic within the dendrites.When△T=150 K,a cell-like solidification morphology can be found,which can be proposed to be formed based on the nucleation and growth of spinodal decomposition mechanism.When△T=250 K,there is a strong direction of the solidification under an optical micrograph,two zones can be divided,and the microstructure of each zone presents a network which results from a liquid spinodal decomposition.When△T=320 K,the microstructure presents a random network completely.Microhardness test shows that the hardness of the solidified specimens increases with the undercooling.