铸态合金组织分析 第一讲 组织组成物的特征

从本期开始我们将分期刊出由唐孝杰与夏建元两位同志联合撰写的“铸态合金组织分析”的专题讲话。本专题共分五讲刊出,其五讲分别为:第一讲 组织组成物的特征;第二讲 组织组成物的分析;第三讲 铸态合金组织分析方法;第四讲 铸钢铸铁组织分析实例;第五讲 有色合金组织分析实例。 在工业生产中,我们将会遇到大量的铸件,掌握铸态组织的分析方法,对于合金成分的设计、生产、工艺的制订,以及确保产品质量都具有十分重要的意义。我们希望此专题讲座的内容对广大理化检验工作者能得到启发与帮助。广大读者对本讲座的内容安排有何意见或建议欢迎与我们联系。

Analysis of phase in Cu-15%Cr-0.24%Zr alloy

The vacuum medium-frequency induction melting technology was employed to prepare the Cu-15%Cr-0.24%Zr alloy. The scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）, transmission electron microscopy （TEM） and high-resolution transmission electron microscopy （HRTEM） were used to analyze the phase composition, morphology and structure of the alloy. The results reveal that the as-cast structure of the alloy consists of Cu matrix, Cr dendrite, eutectic Cr and Zr-rich phase. A large number of Cr-precipitated phases occur in the Cu matrix, and Cu5Zr particles can be found in the grain boundary of Cu matrix. The HRTEM images prove that there is a semi-coherent relationship between Cu5Zr and Cu matrix.

Fracture behavior and microstructure of as-cast NiTi shape memory alloy

The as-cast ingot of equiatomic nickel-titanium shape memory alloy （NiTi SMA） was prepared by vacuum consumable arc melting. The tensile tests and the compressive tests with respect to as-cast NiTi SMA were performed to study its mechanical properties of fracture. The microanalysis of as-cast NiTi SMA as well as its fractured samples was performed so as to better understand microstructure evolution and fracture behavior of NiTi SMA. Under tensile loading, the as-cast NiTi SMA shows higher plasticity and is characterized by ductile fracture at 750℃, but it demonstrates poorer plasticity and is characterized by cleavage fracture as well as transcrystalline fracture at room temperature and -100 ℃. Under compressive loading at -100 ~C, the as-cast NiTi SMA is characterized by shear fracture where the normal to the shearing fracture surface inclines about 45° to the compressive axis, and belongs to cleavage fracture where the cracks exoand via transcrvstalline fracture.

Effects of minor Sr, Sn and Sc addition on as-cast microstructure and mechanical properties of ZA84 magnesium alloy

The effects of minor Sr, Sn and Sc addition on the as-cast microstructure and mechanical properties of the ZA84 magnesium alloy were compared. The results indicate that addition of 0.1%Sr, 0.5%Sn or 0.3%Sc (mass fraction) to the ZA84 alloy can refine the grains of the alloy. Furthermore, addition of 0.1%Sr to the ZA84 alloy does not obviously change the morphology and distribution of Mg32(Al,Zn)49 phase. However, addition of 0.5%Sn or 0.3%Sc not only refines and modifies the Mg32(Al,Zn)49 phase but also suppresses the formation of Mg32(Al,Zn)49 phase, especially with the addition of 0.3%Sc. Furthermore, addition of 0.1%Sr, 0.5%Sn or 0.3%Sc to the ZA84 alloy improves the tensile properties at room temperature and 150℃, especially with the addition of 0.1%Sr and 0.3%Sc. However, addition of 0.1%Sr is not beneficial to the creep properties, and addition of 0.5%Sn has no obvious influence on the creep properties. Oppositely, addition of 0.3%Sc to the ZA84 alloy greatly improves the creep properties.

Effects of calcium addition on as-cast microstructure and mechanical properties of Mg-5Zn-5Sn alloy

The effects of Ca addition on the as-cast microstructure and mechanical properties of the Mg-5Zn-5Sn (mass fraction,%) alloy were investigated.The results indicate that an addition of 0.5%-1.5% (mass fraction) Ca to the Mg-5Zn-5Sn alloy not only refines the as-cast microstructure of the alloy but also causes the formation of the primary and/or eutectic CaMgSn phases with high thermal stability;an increase in Ca amount from 0.5% to 1.5% (mass fraction) increases the amount and size of the CaMgSn phase.In addition,Ca addition to the Mg-5Zn-5Sn alloy improves not only the tensile properties at room temperature and 150 ℃ but also the creep properties.Among the Ca-containing Mg-5Zn-5Sn alloys,the one added 0.5% (mass fraction) Ca obtains the optimum ultimate tensile strength and elongation at room temperature and 150 ℃,however,the alloy added 1.5% (mass fraction) Ca exhibits the optimum yield strength and creep properties.

Effect of Sn content on microstructure and tensile properties of as-cast and as-extruded Mg-8Li-3Al-(1,2,3)Sn alloys

The effects of Sn content on microstructure and tensile properties of as-cast and as-extruded Mg-8Li-3Al-(1,2,3)Sn(wt.%)alloys were investigated by X-ray diffractometry(XRD),optical microscopy(OM),scanning electron microscopy(SEM)and tensile test.It is found that,as-cast Mg-8Li-3Al-(1,2,3)Sn alloys consist ofα-Mg+β-Li duplex matrix,MgLiAl2 and Li2Mg Sn phases.Increasing Sn content leads to grain refinement ofα-Mg dendrites and increase in content of Li2MgSn phase.During hot extrusion,complete dynamic recrystallization(DRX)takes place inβ-Li phase while incomplete DRX takes place inα-Mg phase.As Sn content is increased,the volume fraction of DRXedα-Mg grains is increased and the average grain size of DRXedα-Mg grains is decreased.Increasing Sn content is beneficial to strength but harmful to ductility for as-cast Mg-8Li-3Al-(1,2,3)Sn alloys.Tensile properties of Mg-8Li-3Al-(1,2,3)Sn alloys are improved significantly via hot extrusion and Mg-8Li-3Al-2Sn alloy exhibits the best tensile properties.

Microstructure features and mechanical/electrochemical behavior of directionally solidified Al−6wt.%Cu−5wt.%Ni alloy

The effects of the addition of 5.0 wt.%Ni to an Al−6wt.%Cu alloy on the solidification cooling rate(T),growth rate(V_(L)),length scale of the representative phase of the microstructure,morphology/distribution of intermetallic compounds(IMCs)and on the resulting properties were investigated.Corrosion and tensile properties were determined on samples solidified under a wide range of T along the length of a directionally solidified Al−6wt.%Cu−5.0wt.%Ni alloy casting.Experimental growth laws were derived relating the evolution of primary(λ_(1))and secondary(λ_(2))dendritic spacings with T and V_(L).The elongation to fracture(δ)and the ultimate tensile strength(σ_(U))were correlated with the inverse of the square root of λ_(1) along the length of the casting by Hall−Petch type experimental equations.The reinforcing effect provided by the addition of Ni in the alloy composition is shown to surpass that provided by the refinement of the dendritic microstructure.The highest corrosion resistance is associated with a microstructure formed by thin IMCs evenly distributed in the interdendritic regions,typical of samples that are solidified under higher T.

Effects of titanium addition on structural, mechanical, tribological, and corrosion properties of Al-25Zn-3Cu and Al-25Zn-3Cu-3Si alloys

To investigate the effect of grain refinement on the material properties of recently developed Al-25 Zn-3 Cu based alloys,Al-25 Zn-3 Cu,Al-25 Zn-3 Cu-0.01 Ti,Al-25 Zn-3 Cu-3 Si and Al-25 Zn-3 Cu-3 Si-0.01 Ti alloys were produced by permanent mold casting method.Microstructures of the alloys were examined by SEM.Hardness and mechanical properties of the alloys were determined by Brinell method and tensile tests,respectively.Tribological characteristics of the alloys were investigated by a ball-on-disc type test machine.Corrosion properties of the alloys were examined by an electrochemical corrosion experimental setup.It was observed that microstructure of the ternary A1-25 Zn-3 Cu alloy consisted ofα,α+ηandθ(Al2Cu)phases.It was also observed that the addition of 3 wt.%Si to A1-25Zn-3Cu alloy resulted in the formation of silicon particles in its microstructure.The addition of 0.01 wt.%Ti to the Al-25Zn-3Cu and Al-25 Zn-3 Cu-3 Si alloys caused a decrement in grain size by approximately 20%and 39%and an increment in hardness from HRB 130 to 137 and from HRB 141 to 156,respectively.Yield strengths of these alloys increased from 278 to 297 MPa and from 320 to 336 MPa while their tensile strengths increased from 317 to 340 MPa and from 334 to 352 MPa.Wear resistance of the alloys increased,but corrosion resistance decreased with titanium addition.

Microstructure evolution of semi-solid Mg-14Al-0.5Mn alloys during isothermal heat treatment

A new Mg-14Al-0.5Mn alloy that exhibits a wide solidification range and sufficient fluidity for semi-solid forming was designed. And the rnicrostructure evolution of semi-solid Mg-14Al-0.5Mn alloy during isothermal heat treatment was investigated. The mechanism of the microstructure evolution and the processing conditions for isothermal heat treatment were also discussed. The results show that the microstructures of cast alloys consist of α-Mg,β-Mg17Al12 and a small amount of Al-Mn compounds. After holding at 520 ℃ for 3 min, the phases of β-Mg17Al12 and eutectic mixtures in the Mg-14Al-0.5Mn alloy melt and the microstructures of α-Mg change from developed dendrites to irregular solid particles. With increasing the isothermal time, the amount of liquid increases, and the solid particles grow large and become spherical. When the holding time lasts for 20 min or even longer, the solid and liquid phases achieve a state of dynamic equilibrium.

Compocasting of A356-CNT composite

A356 aluminum alloys reinforced with carbon nano-tubes (CNTs) were produced by stir casting and compocasting routes and their microstructural characteristics and hardness were examined.In order to alleviate the problems associated with poor wettability, agglomeration and gravity segregation of CNTs in the melt, CNTs were introduced into the melts by injection of CNT deposited aluminum particles instead of raw CNTs.Aluminum particles with mean diameters of less than 100 μm were first deposited by CNTs using Ni-P electroless plating technique and then injected into the melt agitated by a mechanical stirrer.The slurry was subsequently cast at temperatures corresponding to full liquid as well as 0.15 and 0.30 solid fractions.The results show that addition of CNTs to A356 matrix can significantly refine both full liquid and semi-solid cast microstructures.Hardness of the samples is also significantly increased by addition of CNTs and A356-CNT composite cast at 0.3 solid fraction produces the highest hardness.

Feasibility of semi-solid die casting of ADC12 aluminum alloy

The feasibility of semi-solid die casting of ADC12 aluminum alloy was studied. The effects of plunger speed, gate thickness, and solid fraction of the slurry on the defects were determined. The defects investigated are gas and shrinkage porosity. In the experiments, semi-solid slurry was prepared by the gas-induced semi-solid （GISS） technique. Then, the slurry was transferred to the shot sleeve and injected into the die. The die and shot sleeve temperatures were kept at 180 ℃ and 250 ℃, respectively. The results show that the samples produced by the GISS die casting give little porosity, no blister and uniform microstructure. From all the results, it can be concluded that the GISS process is feasible to apply in the ADC12 aluminum die casting process. In addition, the GISS process can give improved properties such as decreased porosity and increased microstructure uniformity.

Microstructure and mechanical properties of cast and heat treated Ti-6.55Al-3.41Mo-1.77Zr alloy

α＋βtitanium alloy with a composition of Ti-6.55Al-3.41Mo-1.77Zr （mass fraction,%） was cast into bars in a graphite mould using vacuum induction skull melting furnace （ISM）. The cast bars were hot swaged at 700 °C and then heat treated by two different regimes which resulted in fine and coarse lamella structures, respectively. The grain size of the as-cast structure was estimated to be 660 μm and the swaged samples obtained a very fine grain size in the range of 50 μm. The overall best combination of hardness, tensile properties, and wear resistance of theα＋βtitanium alloy was achieved by heat treating the samples at 1050 °C for getting fine lamellar structure. The maximum compression strength was reported for the heat treated samples at 800 °C with coarse lamella structure. The minimum wear rate was reported for the heat treated samples with fine lamellar structure and the maximum wear rate was obtained for as-cast samples due to its coarse and heterogeneity microstructure.