稀土Nd对铸造铝硅合金变质作用的长效性及重熔性研究

以稀土元素Nd为变质剂,采用金属型铸造工艺制备铸造铝硅合金ZL101,并通过金相显微镜、扫描电镜、布氏硬度计和电子万能试验机研究变质时间及重熔次数对合金显微组织和力学性能的影响.结果表明,稀土Nd对合金具有较好的变质作用,并具有长效性和重熔性,变质6h及重熔4次后合金中的共晶硅组织仍呈小片状的变质状态,且合金硬度及拉伸性能均未受明显影响.变质不同时间及重熔不同次数的合金拉伸试样均为解理断裂.     

Grain coarsening in semi-solid state and tensile mechanical properties of thixoformed AZ91D-RE

For thixoforming to be possible,the microstructure of the starting material must be non-dendritic,which can be obtained by the strain induced melt activation(SIMA)route.Based on the SIMA route,as-cast AZ91D alloy with the addition of yttrium was deformed by cyclic closed-die forging(CCDF).Microstructure evolution of CCDF formed AZ91D-RE alloy during partial remelting were investigated.Furthermore,the mechanical properties of thixoformed AZ91D-RE magnesium alloy components were also studied.The results showed that prolonged holding time resulted in grain coarsening and the improvement in degree of spheroidization.The coarsening behaviour of solid grains in the semi-solid state obeyed Ostwald ripening mechanism.The coarsening rate constant of CCDF formed AZ91D-RE during partial remelting was 324 um3/s at 550℃.The value of yield strength,ultimate tensile strength and elongation to fracture of four-pass CCDF formed AZ91D-RE magnesium alloy were 214.9,290.5 MPa and 14%,respectively.Then the four-pass CCDF formed alloys were used for thixoforming.After holding at 550℃ for 5 min,the values of yield strength,ultimate tensile strength and elongation to fracture of thixoformed component were 189.6 MPa,274.6 MPa and 12%,respectively.However,prolonged holding time led to remarkable decrease in mechanical properties of thixoformed components.     

稀土对HAl62-3-3-0.7合金组织和性能的影响

通过对合金成分的调整分别配制了添加不同量稀土元素的试验用HAl62-3-3-0．7合金。借助金相与扫描电镜观察和分析了各合金的显微组织结构，运用模拟设备测试了各合金的力学性能。文章阐述了稀土元素对该类高强度耐磨黄铜的组织和性能的影响，试验表明适量加入稀土会显著细化晶粒，过量的稀土会导致在合金显微组织中形成线形富稀土相。随着合金中稀土含量的增加，合金的硬度升高，但当稀土含量超过0．1％时，由于线形富稀土相的形成，反而会使合金的力学性能下降。     

Influence of Cerium and Yttrium on Cu-Cr-Zr Alloys

Testing results shows that alloying with Ce and Y improves the hardness and softens temperature of cold worked Cu-Cr-Zr alloys obviously, while the conductivity was fluctuant with the variation of RE content. Observation and analysis indicate that micro-dosage RE elements helps to refine microstructure and morphology of Cu-Cr-Zr-RE alloys, suppress microstructure coarsening and improves homogeneous level of Cu-Cr-Zr alloys. Alloying with 0.01% Ce causes about 1% IACS increment of conductivity, and reduces about 2%～3.5% IACS conductivity after alloying with 0.03%～0.04% RE (Ce or Ce Y) for Cu-Cr-Zr alloys. The microstructure of as-cast Cu-Cr-Zr alloy is refined after alloying with 0.01% Ce while the plasticity is improved slightly. Alloying with 0.01%～0.04% RE improves the softening temperature of deformed Cu-Cr-Zr alloys about 20～40 K; hardness is also improved about 20～35 HV. Test data indicate that alloying with Ce Y raises softening temperature and hardness of Cu-Cr-Zr alloys more notably than alloying with pure Ce.     

稀土变质剂对铸造铝合金性能的影响

采用正变试验法，探讨了稀土变质剂对铸造结合金ZL102性能提高的可行性．试验选用了不同的稀土添加量，考察了不同的变质时间及热处理制度对ZL102的强度、硬度、流动性以及重熔性等性能的综合影响规律．试验表明，稀土是铸造铝合金的优良变质剂，并且添加单一稀土的变质效果优于混合稀土．     

Effects of La-Rich Rare Earth Alloys on Structure and Mechanical Properties of ZL101A Alloy

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Effects of RE on Microstructures and Mechanical Properties of Hot-Extruded AZ31 Magnesium Alloy

Effects of rare earth (RE) additions on microstructure and mechanical properties of the wrought AZ31 magnesium alloy were investigated. The results show that, by adding 0.3%, 0.6% and 1.0% RE elements, the as-cast microstructure can be refined, and the as-cast alloys‘ elongation and tensile strength can be improved. After extrusion, the alloy with 0.3 % and 0.6% RE additions obtain a finer microstructure and the best mechanical properties, but the alloy with 1.0% RE addition has the coarse A1-RE compound particles in grain boundaries which decreased elongation and tensile properties. Usually, Rare earth (RE) elements were used to improve the creep properties of aluminium-containing magnesium pressure die cast alloys at elevated temperatures. In this paper, it is also found that the high temperature strength of extruded materials can be increased by RE elements additions.     

Rheological behavior of Al-Mg-Si-Cu alloys in the mushy state obtained by partial remelting and partial solidification at high cooling rate

This work investigates the mechanical behavior of two aluminum alloys in the mushy state, the alloy AA6056 and an alloy based on mixing AA6056 and AA4047. These alloys have been studied to give insight into the susceptibility to hot tearing, which occurs during laser welding of AA6056 with 4047 filler wire. Two types of isothermal tensile tests have been conducted: (1) tests during partial remelting and (2) tests after partial solidification at a high cooling rate. Results show that the maximum tensile stress increases with increasing solid volume fraction. Both materials exhibit visco-plastic behavior for solid fractions in the range 0.9 to 0.99, except for a critical solid fraction of 0.97, where the semisolid material also shows minimum ductility. The stress levels observed for the remelting experiments are larger than those found for partial solidification experiments at the same solid fraction due to the influence of the microstructure. The influence of temperature and strain rate on the maximum stress is described by using a constitutive law that takes into account the fraction of grain boundaries wetted by the liquid.     

添加钕对Mg2Ni储氢合金的结构和电极性能的影响

利用两步法制备了一系列添加Nd的三元Mg2-xNdxNi合金。XRD分析证实，当x=0．05，0．1时，制得的三元Mg2-xNdxNi合金均为Mg2Ni单相合金；三元Mg18Nd0．2Ni(x=0．2，0．3)合金为三相合金，三相分别为Mg2Ni，NdNi，NdMgNi4。模拟电池测试结果表明，同Mg2Ni合金相比，球磨10h的三元Mg1．8Nd0．2Ni合金和Mg17Nd03Ni合金电极的放电容量提高明显，且Mg17Nd03Ni合金电极的循环性能有明显改善。这极有可能与合金中NdMgNi4相的存在以及球磨形成的微结构有关。     

Microstructure of Al-5Ti-1B-1RE nanoribbon and its refining efficiency on as-cast A356 alloys

The novel Al-5Ti-1B-1RE nanoribbons were synthesized by melt-spinning.The microstructure showed that the Al-5Ti-1B-1RE nanoribbon consisted of granular-like TiB2 and core-shell-like TiAl3/Ti2Al20Ce.The Al-5Ti-1B-1RE nanoribbon could give rise to the excellent refining effect on as-cast A356 alloys.The refining efficiency and formation mechanism of Al-5Ti-1B-1RE nanoribbons were investigated.In accordance with the experimental results,it could be seen that the Al-5Ti-1B-1RE nanoribbon could maintain the refining effect after 60 min of holding.Additionally,owing to the addition of Al-5Ti-1B-1RE nanoribbon,the mechanical properties of A356 alloys could be enhanced significantly.     

Influence of Nd and Y additions on the corrosion behaviour of extruded Mg-Zn-Zr alloys

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.     

Rapid graphitization of a pulsed laser remelted ductile cast iron during multipass overlap melting

As-cast ductile cast iron with an as-machined shiny metal surface was remelted with a high-power (1 kW) pulsed Nd:YAG laser using both single- and multipass overlap melt tracks. Changes in the microstructure of the underlying laser melted track caused by the transient overlap heating during multipass overlap remelting process were studied. The rapidly solidified metastable ledeburite structure of the underlying laser melted track was found to be rapidly graphitized during overlap remelting. The graphitized zone consists of a fully graphitized zone containing extremely fine graphite nodules and a partially graphitized zone containing extremely fine graphite nodules and undissolved cementite. The overlap ratios of the melt tracks were shown to have no noticeable influence on either the graphitized microstructure and the size of the graphitization zones. This newly observed rapid graphitization phenomenon is preliminarily discussed in terms of the microstructural characteristics of the rapidly solidified ductile iron and the unique heating behavior of pulsed laser beam to material.     

Effect of Yttrium on Microstructures and Preparation and Structure of Mg2-xRExNi (RE=La,Ce,Pr,Nd,Y) Ternary Alloys

A series of Mg2-xNdxNi(x=0.05,0.1,0.2,0.3)alloys and Mg1.95RE0.05Ni(RE= La,Ce,Pr,Nd,Y)ternary alloys were prepared by ball milling of mixted powder of Mg,Ni,RE and sintering under the protection of argon.XRD analysis shows that Mg2-xNdxNi(x=0.05,0.1)and Mg1.95RE0.05Ni consist of single phase with the same crystal structure as Mg2Ni.While three-phase alloys including Mg2Ni,NdNi and NdMgNi4 were formed in Mg1.8Nd0.2Ni and Mg1.7Nd0.3Ni alloys respectively.The lattice constants of Mg2Ni in those ternary alloys were calculated.The decomposition of Mg2Ni occurs in the milling process of Mg2Ni and Mg1.95RE0.05 Ni alloys respectively.For the latter,another earlier reaction occurs in milling process,which means that atoms of RE are separated from crystal structure of Mg2Ni and form relevant oxides by combination with oxygen existed in argon atmosphere.     

重熔保温时间对Al-Ti-C中间合金微观组织及细化性能的影响

利用Al、Ti、C粉末原料,采用铝熔体热爆法合成了相同成分不同微观组织形貌的两种Al-Ti-C中间合金晶粒细化剂。借助X射线衍射(XRD)、大型光学显微镜(MEF3)等分析手段研究了重熔保温时间对Al-Ti-C中间合金微观组织及细化效果的影响。结果表明:合成的两种Al-Ti-C中间合金均由Al、TiAl3和TiC组成。重熔时,保温时间对Al-Ti-C中间合金微观组织产生重要影响。随着重熔保温时间的延长,TiAl3会发生聚集、长大,而TiC颗粒有聚集倾向,但保温过程中,TiAl3和TiC相表现出较强的稳定性,并没有生成其他杂相如Al4C3等。重熔后的Al-Ti-C中间合金仍具有一定的晶粒细化能力。     

稀土在银饰品材料中作用的研究

为改善银合金饰品材料的抗自然时效软化和抗变色性能,试验研究了含稀土(钇、镧、铈)低于0.11%的银合金饰品材料,测试了银合金的硬度随变形量、温度及时效时间的变化规律,并用电子探针对银饰品试样进行扫描分析,在0.1mol/L的硫化钠水溶液中对各试样进行了腐蚀实验,发现银钇固溶态银合金比纯银具有较好的耐腐蚀性能和较高的抗时效软化能力,适合于用作银饰品材料,而含有弥散分布的第二相稀土化合物的银合金则显示了更好的加工硬化和抗时效软化效果,但其抗硫化变色能力则不如纯银.     

Grain refinement of Mg-3Y alloy using Mg-10Al_2Y master alloy

The as-extruded Mg-10 Al_2 Y master alloy was chosen as a novel grain refiner for as-cast Mg-3 Y alloy.Contrast samples of cast Mg-3 Y alloy added with pure Al and Mg-Zr master alloy grain refiners were prepared under the same conditions.In this study,the influence of addition amounts of Al_2 Y and holding time on grain refinement efficiency as well as tensile properties was investigated.And the grain refining ability of the Al_2 Y particles was systematically evaluated in terms of the addition amounts,number density of the Al_2 Y particles and holding time.The finest grains are achieved at 2 wt% Al_2 Y addition amount,which corresponds to number density of the polygonal Al_2 Y particles of 420-460 mm~(-2).The Mg-10 Al_2 Y master alloy has significant refinement performance and no refining recession occurs at the holding time within 60 min,or the settling time up to 180 min.Grain refinement and the second phase strengthening of uniformly distributed Al_2 Y particles contribute to the simultaneous enhancement on both strength and elongation of Mg-3 Y alloy.     

Microstructure and mechanical properties of Mg-7Zn-3Al alloy with Nd and Y additions

The effects of combined addition of 0.6 wt.% Nd and 0.4 wt.% Y on the microstructure and mechanical properties of Mg-7Zn-3Al alloy were investigated.The results indicated that the Nd and Y addition led to obvious dendrite coarsening.However,it could modify the morphology and distribution of-Mg 32(Al,Zn) 49 intermetallics.Moreover,Al 2 REZn 2 phase could be introduced into the alloy with the Nd and Y addition.With the effective second-phase strengthening,the ultimate tensile strength and elongation in as-cast state can be improved by the Nd and Y addition.After ageing treatment,the alloy with the Nd and Y addition exhibited better precipitation strengthening effects by forming finer MgZn 2 and Mg 32(Al,Zn) 49 precipitates into the-Mg matrix.As a result,the yield and ultimate strength of Mg-7Zn3Al-0.6Nd-0.4Y alloy could be increased to 182 and 300 MPa by peak-ageing treatment.     

An experimental investigation on the kinetics of solute driven remelting

The present study is aimed at understanding the interface kinetics during solute driven remelting in metallic alloys. Solid Al is placed in contact with a liquid Al-Mg alloy. As solid and liquid compositions at the interface are out of equilibrium, remelting takes place. The remelting rate is estimated as a function of time using a simple heat balance. The estimated velocity from the heat-balance calculations shows excellent agreement with the geometric velocity, directly measured from the remelted samples in each experiment. This confirms the accuracy and reliability of the heat-balance calculations and establishes this technique as a potential method for tracing the interface velocity during remelting. The results indicate that, at a constant temperature, an increase in liquid supersaturation leads to a linear increase in remelting velocity, as a result of an increasing driving force for remelting. At a constant liquid supersaturation, an increase in temperature results in an exponential increase in the remelting velocity, due to the enhanced mass transport at the higher temperatures. Semi-empirical relations are derived from these experimental observations and a combined analysis of the effects of driving force and kinetics yields a relation for remelting velocity as a function of temperature for a variety of boundary conditions. Remelting velocities predicted by this relation are in good agreement with the experimental observations.     

电热合金钢0Cr21A16NbRE电渣重熔用渣的研究

研究了电热合金钢OCr21A16NbRE电渣重熔用渣70%CaF₂-25%Al₂O₃-5%CaO在正常重熔制度下（A=2800 A,V=30 V）液态炉渣自然冷却与经过渣钢反应后冷却至固相渣的各部位成分与物相,分析了钢液中稀土元素的烧损。结果表明,液渣冷却的固相中不含稀土元素,其成分点位于CaF₂-CaO·2Al₂0₃-Ca0·6Al₂0₃组成的子三角形内,各层化学成分和物相不同,但以CaF₂为主。炉渣经渣钢反应后可分为五层,颜色、物相各不相同;CaF2含量最高部位在上两层,Al₂O₃含量从无到有逐层升高;各层均检测到稀土氧化物,中间层及最底层（钢液滴落处）含量较高,稀土相中以铈镧的铝酸盐（Ce,La）x（AlO₂）y为主相,该相结构致密硬度高。计算表明,在中下层区域,炉渣氧化性较强,钢中稀土元素主要在此部位被氧化。增加渣中Y₂0₃量有利于提高电渣锭中稀土元素Y的含量。     

电渣连铸技术的开发

在结合电渣重熔和连铸技术优点的基础上。东北大学钢铁冶金研究所采用双极串联、交换电极及在线切割等技术，在国内首次成功地开发了电渣连铸（ESCC）技术；解决了电渣重熔钢锭直径小于300mm时熔速很慢、冶炼费用很高的难题。通过对重熔方坯质量的低倍、高倍、夹杂物检验等分析表明，该技术生产的方坯表面质量和内部质量良好，具有广泛应用前景和经济价值。