Review of Sc microalloying effects in Al-Cu alloys

Artificially controlling the solid-state precipitation in aluminum (Al) alloys is an efficient way to achieve well-performed properties,and the microalloying strategy is the most frequently adopted method for such a purpose.In this paper,recent advances in lengthscale-dependent scandium (Sc) microalloying effects in Al-Cu model alloys are reviewed.In coarse-grained Al-Cu alloys,the Sc-aided Cu/Sc/vacancies complexes that act as heterogeneous nuclei and Sc segregation at the θ′-Al_(2)Cu/matrix interface that reduces interfacial energy contribute significantly to θ′precipitation.By grain size refinement to the fine/ultrafine-grained scale,the strongly bonded Cu/Sc/vacancies complexes inhibit Cu and vacancy diffusing toward grain boundaries,promoting the desired intragranular θ′precipitation.At nanocrystalline scale,the applied high strain producing high-density vacancies results in the formation of a large quantity of (Cu Sc,vacancy)-rich atomic complexes with high thermal stability,outstandingly improving the strength/ductility synergy and preventing the intractable low-temperature precipitation.This review recommends the use of microalloying technology to modify the precipitation behaviors toward better combined mechanical properties and thermal stability in Al alloys.

Development in oxide metallurgy for improving the weldability of high -strength low-alloy steel-Combined deoxidizers and microalloying elements

The mechanisms of oxide metallurgy include inducing the formation of intragranular acicular ferrite(IAF)using micron-sized inclusions and restricting the growth of prior austenite grains(PAGs)by nanosized particles during welding.The chaotically oriented IAF and refined PAGs inhibit crack initiation and propagation in the steel,resulting in high impact toughness.This work summarizes the com-bined effect of deoxidizers and alloying elements,with the aim to provide a new perspective for the research and practice related to im-proving the impact toughness of the heat affected zone(HAZ)during the high heat input welding.Ti complex deoxidation with other strong deoxidants,such as Mg,Ca,Zr,and rare earth metals(REMs),can improve the toughness of the heat-affected zone(HAZ)by re-fining PAGs or increasing IAF contents.However,it is difficult to identify the specific phase responsible for IAF nucleation because ef-fective inclusions formed by complex deoxidation are usually multiphase.Increasing alloying elements,such as C,Si,Al,Nb,or Cr,con-tents can impair HAZ toughness.A high C content typically increases the number of coarse carbides and decreases the potency of IAF formation.Si,Cr,or Al addition leads to the formation of undesirable microstructures.Nb reduces the high-temperature stability of the precipitates.Mo,V,and B can enhance HAZ toughness.Mo-containing precipitates present good thermal stability.VN or V(C,N)is ef-fective in promoting IAF nucleation due to its good coherent crystallographic relationship with ferrite.The formation of the B-depleted zone around the inclusion promotes IAF formation.The interactions between alloying elements are complex,and the effect of adding dif-ferent alloying elements remains to be evaluated.In the future,the interactions between various alloying elements and their effects on ox-ide metallurgy,as well as the calculation of the nucleation effects of effective inclusions using first principles calculations will become the focus of oxide metallurgy.

碳钢Cr-Ti共渗及Al-Ti共渗层的组织和性能

为了提高碳钢构件的硬度、耐磨性和耐蚀性,对35钢及20钢实施Cr Ti共渗及Al Ti共渗,用X射线、EPMA、显微硬度及摩擦磨损实验等分析测试方法,研究了渗层的组织和性能.结果表明,35钢Cr Ti共渗层外侧富Cr、内侧富Ti,在3.5%NaCl和10%H2SO4溶液中有良好的耐蚀性;渗层表面硬度HV0.2=1900,耐磨性比17Cr2Ni2Mo渗碳钢对比试样提高3倍.35钢Al Ti共渗层外侧富Ti、内侧富Al,在10%H2SO4溶液中的耐蚀性较差;渗层表面硬度为HV0.2=400,但耐磨性仍比对比试样提高近一倍.

35碳钢Cr-Ti共渗及Al-Ti共渗层的高温氧化行为

用循环氧化法测定了35钢Cr Ti及Al Ti共渗层的抗高温氧化性能.Cr Ti共渗层内侧富集的Ti以稳定的TiC形式存在,阻碍了表层富集的Cr向内层扩散,在700、800℃×96h条件下的抗高温氧化性能与0Cr18Ni9不锈钢接近.Al Ti共渗层内侧富Al,外侧富Ti.但经24h氧化加热后,Al、Ti元素的分布发生逆转,Al向表面富集,而Ti在渗层内侧富集并形成TiC,使氧化增重速率明显下降.如果以24h氧化加热后的氧化增重速率为比较标准,Al Ti共渗层在900℃×96h的抗高温氧化性能优于Cr Ti共渗.

Effect of V and V-N Microalloying on Deformation-Induced Ferrite Transformation in Low Carbon Steels

Deformation-induced ferrite transformation （DIFT） has been proved to be an effective approach to refine ferrite grains. This paper shows that the ferrite grains can further be refined through combination of DIFT and V or V-N microalloying. Vanadium dissolved in γ matrix restrains DIFT. During deformation, vanadium carbonitrides rapidly precipitate due to strain-induced precipitation, which causes decrease in vanadium dissolved in matrix and indirectly accelerates DIFT. Under heavy deformation, deformation induced ferrite （DIF） grains in V microalloyed steel were finer than those in V free steel. The more V added to steel, the finer DIF grains obtained. Moreover, the addition of N to V microalloyed steels can remarkably accelerate precipitation of V, and then promote DIFT. However, DIF grains in V-N microalloyed steel easily coarsen.

Role of multi-microalloying by rare earth elements in ductilization of magnesium alloys

The present work investigates the influences of microalloying with rare earths on the mechanical properties of magnesium alloys.The amount of each rare earth element is controlled below 0.4 wt.%in order not to increase the cost of alloy largely.The synergic effects from the multi-microalloying with rare earths on the mechanical properties are explored.The obtained results show that the as-cast magnesium alloys multi-microalloying with rare earths possesses a quite high ductility with a tensile strain up to 25-30%at room temperature.Moreover,these alloys exhibit much better corrosion resistance than AZ31 alloy.The preliminary in situ neutron diffractions on the deformation of these alloys indicate that the multi-microalloying with rare earths seems to be beneficial for the activation of more slip systems.The deformation becomes more homogeneous and the resultant textures after deformation are weakened.

Tailoring the microstructural characteristic and improving the corrosion resistance of extruded dilute Mg-0.5Bi-0.5Sn alloy by microalloying with Mn

Mg-0.5Bi-0.5Sn alloys with and without microalloying with 0.5 wt%Mn were subjected to extrusion,and the effect of Mn microalloying on the microstructural characteristic and corrosion behavior of the extruded alloys was investigated.The results indicated that the average grain size and the density of dislocations decreased,and a new Mg_(26.67)Mn_(65.47)Fe_(7.86)second phase as well as grain boundary segregation of Sn atoms could be observed in certain micro-regions of the extruded dilute Mg-0.5Bi-0.5Sn-0.5 Mn alloy.The tailoring of microstructure resulted in the significant enhancement in corrosion resistance(R_(p)increased from 1095.91Ωcm^(2)to 5008.79Ωcm^(2)).In addition,grain boundary segregation resulted in intergranular corrosion and led to the dissolution of Sn atoms.Hence,the dissolution rate of the matrix in Mg-0.5Bi-0.5Sn-0.5Mn alloy could be inhibited by the corrosion product film containing an intermediate product(SnO_(2)).

STRUCTURE CHARACTERISTICS OF MICROALLOYING AS-CAST MARTENSITIC CAST IRON

The microstructure and martensite substructure of as-cast martensitic high-Cr cast iron by injection microalloying have been studied by usig SEM and TEM.The relationship between distribution of alloying elements and phase formation of carbide,as well as various branching and distortion of carbide,have been analysed by X-ray diffractometer and EPMA.

Titanium microalloying of steel:A review of its effects on processing,microstructure and mechanical properties

Carbon neutrality of the steel industry requires the development of high-strength steel.The mechanical properties of low-alloy steel can be considerably improved at a low cost by adding a small amount of titanium(Ti)element,namely Ti microalloying,whose performance is related to Ti-contained second phase particles including inclusions and precipitates.By proper controlling the precipitation behaviors of these particles during different stages of steel manufacture,fine-grained microstructure and strong precipitation strengthening effects can be obtained in low-alloy steel.Thus,Ti microalloying can be widely applied to produce high strength steel,which can replace low strength steels heavily used in various areas currently.This article reviews the characteristics of the chemical and physical metallurgies of Ti microalloying and the effects of Ti microalloying on the phase formation,microstructural evolution,precipitation behavior of low-carbon steel during the steel making process,especially the thin slab casting and continuous rolling process and the mechanical properties of final steel products.Future development of Ti microalloying is also proposed to further promote the application of Ti microalloying technology in steel to meet the requirement of low-carbon economy.

Microstructure and mechanical properties of the welding joint filled with microalloying 5183 aluminum welding wires

In this study, 7A52 aluminum alloy sheets of 4 mm in thickness were welded by tungsten inert gas welding using microalloying welding wires containing traces of Zr and Er. The influence of rare earth elements Zr and Er on the microstructure and mechanical properties of the welded joints was analyzed by optical microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, hardness testing, and tensile mechanical properties testing. Systematic analyses indicate that the addition of trace amounts of Er and Zr leads to the formation of fine Al3Er, Al3Zr, and Al3（Zr,Er） phases that favor significant grain refinement in the weld zone. Besides, the tensile strength and hardness of the welded joints were obviously improved with the addition of Er and Zr, as evidenced by the increase in tensile strength and elongation by 40 MPa and 1.4%, respectively, and by the welding coefficient of 73%.

A comparison study of Ce/La and Ca microalloying on the bio-corrosion behaviors of extruded Mg-Zn alloys

The influences of Ca and Ce/La microalloying on the microstructure evolution and bio-corrosion resistances of extruded Mg-Zn alloys have been systematically investigated in the current study.Compared with single Ca or Ce/La addition,the Ca-Ce/La cooperative microalloying results in an outstanding grain refinement,because the fine secondary phase particles effectively hinder the recrystallized grain growth.The coarse Ca2Mg6Zn3 phases promote the formation of Ca3(PO4)2 or hydroxyapatite particles during the immersion process and accelerate the dissolution of the corrosion product film,which destroys its integrity and results in the deterioration of anti-corrosive performance.The Ce/La elements can be dispersed within the conventional Mg7Zn3 phases,which reduce the internal galvanic corrosion between Mg matrix and the secondary phases,leading to an obvious improvement of corrosion resistance.Therefore,the Ca-Ce/La cooperative microalloying achieves a homogenous fine-grained microstructure and improves the protective ability of surface film,which will pave a new avenue for the design of biomedical Mg alloys in the coming future.

MICROALLOYING EFFECT OF BORON ON COPPER-BASE ALLOYS

The microstructure and properties of boron-modified copper-base alloys were investigated by tension,corrosion,corrosive wear and erosion tests.The results show that by adding boron in copper-base alloys,the strength and hardness of alloys increase,the plasticity decreases somewhat;the corrosion,corrosive wear and erosion resistance of boron-modified copper-base alloys improve obviously.The microalloying mechanism of boron in copper-base alloys was found.

Enhancing corrosion resistance of ZK60 magnesium alloys via Ca microalloying: The impact of nanoscale precipitates

Enhancing corrosion resistance of Mg-Zn alloys with high strength and low cost was critical for broadening their large-scale practical applications. Here we prepared solutionized, peak-and over-aged ZK60 alloys with and without microalloying Ca(0.26 wt.%) to explore the effects of nanoscale precipitates on their corrosion behavior in detail via experimental analyses and theoretical calculations. The results suggested the peak-aged ZK60 alloy with Ca addition showed improved corrosion resistance in comparison with the alloys without Ca,owing to the contribution of Ca on the refinement of precipitates and increase in their number density. Although the precipitates and Mg matrix formed micro-galvanic couples leading to dissolution, the fine and dense precipitates could generate “in-situ pinning” effect on the corrosion products, forming a spider-web-like structure and improving the corrosion inhibition ability accordingly. The pinning effect was closely related to the size and number density of precipitates. This study provided important insight into the design and development of advanced corrosion resistant Mg alloys.

Preventing Occurrence of Transverse Corner Cracks on Nb, V and Ti Microalloying Steel CC Slabs

Based on their hot ductilities, Nb, V and Ti microalloying steels can be classified into two groups. The first group includes steels with lower carbon content (≤0.10%). Ductilities of steels of this group recover and rise with decreasing temperature when temperature lowers to below 825℃. Another group includes steels which contain more carbon (>0.12%) or contain more Nb and V. The low ductility temperature Region Ⅲ for steels of mis group extends to temperature as low as 725℃. The occurrence of the transverse corner cracks of the Nb, V and Ti microalloying steel CC slabs has be considerably decreased by stabilizing casting speed, increasing mold steel level automatic control ratio,enhancing caster segment radial alignment and adopting proper secondary cooling patterns to make slab corner temperature at straightening out off the low ductility temperature region.

Kinetic Monte Carlo simulation of microalloying effect in Al-Ag alloys

The kinetic Monte Carlo method, which based on the Multi-States Ising Model, was applied to simulate the effect of microelements on the microstructural evolution of Al-Ag alloys during initial aging stage. The simulation results suggest that the microelements In, Sn and Be have a dramatic depression effect on the Ag clustering because of their strong tendency to co-existed with vacancies. There are no significant effects on the process of Ag clustering in Al-Ag alloys containing Li or Cd, because of little interaction between Li/Cd and Ag/vacancies. Microelements can influence the aging by interacting with vacancies and the atoms of precipitated composition, in which the former seems more important. In this model, “vacancy-locking” and “vacancy clusters” are two important mechanisms in the aging process.

Effects of Rare-earth and Microalloying Elements on the Microstructure Characteristics of Hypereutectoid Rails

We performed thermal simulation experiments of double-pass deformation of hypereutectoid rails with different microalloying elements at a cooling rate of 1℃/s and deformation of 80%to explore the influence of rare-earth and microalloying elements on the structure of hypereutectoid rails and optimize the composition design of hypereutectoid rails.Scanning electron microscopy,transmission electron microscopy,X-ray diffraction,and other characterization techniques were employed to quantitatively analyzed the effects of different microalloying elements,including rare-earth elements,on pearlite lamellar spacing,cementite characteristics,and dislocation density.It was found that the lamellar spacing was reduced by adding various microalloying elements.Cementite lamellar thickness decreased with the refinement of pearlite lamellar spacing while the cementite content per unit volume increased.Local cementite spheroidization,dispersed in the ferrite matrix in granular form and thus playing the role of dispersion strengthening,was observed upon adding cerium(Ce).The contributions of dislocation density to the alloy strength of four steel sheet samples with and without the addition of nickel,Ce,and Ce–copper(Cu)composite were 26,27,32,and 37 MPa,respectively,indicating that the Ce–Cu composite had the highest dislocation strengthening effect.The Ce–Cu composite has played a meaningful role in the cementite characteristics and dislocation strengthening,which provides a theoretical basis for optimizing the composition design of hypereutectoid rails in actual production conditions.

Ni-Cr-Ti烤瓷合金烤瓷结合性能试验分析

钛（Ti）在牙科被称为理想的修复材料，具有良好的耐腐蚀性和生物相容性。提高原来（Ni—Cr）烤瓷合金的理化性能和生物相容性也成目前研究的焦点。国内也有关于Ni—Cr—Ti烤瓷合金的研制。并应用于临床获得较好效果。由中国医科大学研制的含Ni—Cr—Ti烤瓷合金，与德国VITA瓷粉配套使用，研究其元素成分及含量的变化对金瓷结合的影响。

微合金化元素对Mg-15Gd合金显微组织和耐蚀性能的影响

采用半连续铸造法制备出4种具有不同微合金化元素的Mg-15Gd-0.2X(X=Mn、Ni、Zn、Sn)合金,利用OM、SEM、XRD观察合金微观形貌,分析合金显微组织,通过浸泡腐蚀和析氢实验对合金耐蚀性进行测试,研究不同微合金化元素对Mg-15Gd合金微观组织和耐蚀性能的影响。结果表明,微合金化元素的添加明显改善了合金的铸态组织,细化了晶粒和第二相,并使第二相Mg5Gd沿晶界呈网状分布。添加微量合金化元素后,除Mg-15Gd-0.2Ni合金外,合金的耐蚀性均有明显提高,主要与合金晶粒细化、第二相细化并沿晶界呈网状分布,对合金腐蚀有阻挡作用以及合金腐蚀产物膜完整致密、保护性好有关。

微量Ca对ZE22镁合金显微组织及加工硬化行为的影响

为改善ZE系列镁合金延展性及加工性能,以ZE22为基础合金,通过Ca微合金化改善其加工硬化能力。进行EBSD及室温拉伸试验,研究微量Ca对ZE22镁合金显微组织及加工硬化行为的影响。结果表明:微量Ca的加入可细化晶粒,使平均晶粒尺寸为6.38~8.44μm,并引起基面织构弱化,织构极强度从22.3降至19.2,提高了基面滑移系的施密特因子。微观分析发现,加工硬化的弱化是晶粒尺寸和织构双重作用的结果。微量Ca的加入使合金加工硬化能力和应变率敏感系数降低,ZEG220合金的强塑性匹配更佳。研究结果为微合金化调控镁合金的加工硬化能力提供了理论基础和指导。

晶粒形态对Ti-Mo钢耐蚀性能的影响

采用周期浸润腐蚀实验机、光学显微镜(OM)、扫描电镜(SEM)和电子背散射衍射(EBSD)技术等研究了晶粒形态对Ti-Mo微合金钢耐蚀性能的影响规律。结果表明:Ti-Mo微合金钢经600~750℃等温热处理后的显微组织为单相铁素体,耐蚀性能受晶粒尺寸、大角度晶界比例、再结晶程度的影响;晶界和变形组织作为阳极,晶粒作为阴极,不均匀的电化学腐蚀使实验钢的腐蚀电流升高,促进了电偶腐蚀的发生,这是影响Ti-Mo微合金钢腐蚀行为的主要机制;在不损害力学性能的前提下,可通过采取适当增大晶粒尺寸、降低大角度晶界比例、提高再结晶程度的措施,提高Ti-Mo钢的耐蚀性能;在本实验条件下,当等温温度为600℃时,Ti-Mo钢的晶粒尺寸为9.66μm、大角度晶界比例为80.3%、平均错配角为1.99°、腐蚀质量损失率为1.98 g/(m^(2)·h),其耐蚀性能较高。