Al-3Ti-3B中间合金对AZ31镁合金晶粒细化的影响

利用OM、XRD、SEM和EPMA等手段研究了Al-3Ti-3B细化剂对AZ31镁合金微观组织的影响。结果表明,添加适量的Al-3Ti-3B细化剂能使铸态AZ31镁合金粗大的树枝晶转变为均匀的等轴晶;加入量为0.4%时取得了较好的细化效果,固溶处理后的AZ31镁合金平均晶粒尺寸由300μm减小到50μm。TiB2和AlB2粒子的异质形核作用是促使晶粒细化的主要机制,且TiB2粒子在晶界上的偏聚可进一步阻碍晶粒长大。     

Al-Ti、Al-Ti-C中间合金对AZ91D镁合金组织和性能的影响

研究了Al-5Ti、Al-5Ti-0．25C和Al-8Ti-2C中间合金对AZ91D镁合金的组织、力学性能和耐腐蚀性能的影响。结果表明,添加Al-5Ti中间合金使晶粒粗化,而添加Al-5Ti-0．25C和Al-8Ti-2C中间合金使晶粒细化,Al-8Ti-2C中间舍金的细化效果明显且细化后组织细小均匀;添加Al-5Ti中间合金使合金的力学性能降低,而添加Al-5Ti-0．25C和Al-8Ti-2C中间合金均使合金的拉伸强度和伸长率得到了提高;添加Al-5Ti、Al-5Ti-0．25C和Al-8Ti-2C中间合金均使合金的耐腐蚀性能得到了改善。对于AZ91D合金而言,Al-8Ti-2C中间合金是一种良好的晶粒细化剂。     

Effects of Sb Content on Solidification Pathways and Grain Size of AZ91 Magnesium Alloy

The phase constitution and solidification pathways of AZ91+xSb(x = 0, 0.1, 0.5, 1, in wt%) alloys were investigated through ways of microstructure observation, thermal analysis technique, and thermodynamic calculation. It was found that the non-equilibrium solidification microstructure of AZ91+xSb(x = 0.1, 0.5, 1) is composed of a-Mg matrix, b-Mg17Al12 phase, and intermetallic compound Mg3Sb2. The grain size of the alloys with different Sb contents was quantitatively determined by electron backscattered diffraction technique which shows no grain refinement in Sb-containing AZ91 alloy. Thermodynamic calculations are in reasonable agreement with thermal analysis results, showing that the Mg3Sb2 phase forms after a-Mg nucleation, thus impossible acts as heterogeneous nucleus for a-Mg dendrite. Besides,the solid fraction at dendrite coherency point(fDCPs) determined from thermal analysis decreases slightly with increasing Sb content, which is consistent with the fact that Sb does not refine the grain size of AZ91 alloy.     

Refinement role of electromagnetic stirring and strontium in AZ91 magnesium alloy

Effect of strontium (Sr) addition and electromagnetic stirring on the microstructure of AZ91 alloy and refinement mechanism were investigated. It was found that Sr addition ranging from 0.1 to 0.3 wt.% caused refinement of as-cast microstructure, but did not form any new phases. Combined strontium alloying and electromagnetic stirring significantly decreased the grain size, changed the morphologies of the β-Mg₁₇Al₁₂ phases and reduced their volume percentage. The smallest grain size of AZ91 alloy was obtained in the case of 0.2 wt.%Sr addition with exciting voltage of 100 V. The increase of Vickers hardness (HV) and Brinell hardness (HB) value of AZ91 alloy were as a result of increasing solid solubility of solute elements (Al, Zn) in the matrix and refining-grain strengthening effect. The microstructural refinement was mainly attributed to the increase of the degree of undercooling and nucleation temperature of primary phase on the basis of DTA analysis results.     

Microstructure and tensile properties of magnesium alloy modified by Si/Ca based refiner

Microstructure and mechanical properties of pure magnesium and AZ31 alloy with Ca/Si based refiner addition were investigated. The results indicate that addition of Ca/Si based refiners to pure magnesium and AZ31 alloy results in remarkable microstructure refinement. With proper amount of refiner addition, the grain size in as cast ingots can be one order of magnitude lower than that without refiner addition. Small amount of refiner addition to AZ31 alloy increases both ultimate strength and yield strength significantly,while the ductility of the alloy with refiner addition is similar to that without refiner addition. Addition of refiner improves the deformability of AZ31 alloy and extruded or hot rolled specimens （rods or sheets） with refiner addition exhibit higher surface quality and mechanical properties than those without refiner addition.     

稀土元素对AZ91D合金晶粒细化的影响

研究了不同混合稀土添加量对AZ91D合金晶粒细化的影响。试验结果表明混合稀土对AZ91D合金有明显的细化效果。当混合稀土的添加量为0．05％(质量分数)时，混合稀土中的Ce，Nd和Pr等在未形成A1-RE化合物之前，大部分以质点的形式弥散分布在AZ91D合金熔体中，可能起到非均匀形核的作用；随着混合稀土添加量的增多，RE优先与Al生成A1-RE化合物，这些化合物大部分偏聚在晶界上，阻碍了晶粒的长大，从而细化了晶粒。     

添加SiC对不同尺寸AZ91D镁合金坯料半固态组织的影响

AZ91D镁合金经重熔加入0.3%(质量分数)SiC细化后浇注成不同尺寸(直径)的锭料。研究SiC对不同尺寸AZ91D镁合金坯料半固态等温热处理组织的影响。结果表明:未经SiC细化处理AZ91D镁合金的半固态组织存在明显的尺寸效应,从心部到边缘,固相颗粒尺寸由大逐渐变小,如d70mm试样内的固相颗粒尺寸从心部的150μm变为边缘的110μm,并趋于圆整,液相逐渐增多;随着坯料尺寸的增加,由心部到边缘的组织差异进一步加大。SiC细化的AZ91D镁合金坯料经半固态等温热处理后,其组织中的固相颗粒尺寸整体变得细小,d70mm试样内的固相颗粒均不大于80μm,边缘和心部的固相颗粒尺寸变得很相近,在70μm与80μm之间,球化圆整且分布均匀;经SiC处理的半固态压铸件中,气孔等缺陷明显减少。     

稀土元素镧对AZ91镁合金显微组织及硬度的影响

研究了稀土镧对AZ91合金的显微组织和硬度的影响.结果表明:加入稀土镧后,AZ91合金铸态晶粒细化,且Mg17Al12相减少;大部分镧与铝结合生成高熔点、高热稳定性的针状稀土相(Al11La3),从而改善晶界相的分布,提高铸态宏观硬度;固溶 时效处理后,在晶界处析出片层状Mg17Al12相.随时效时间的延长,硬度进一步增加.     

Mg-8Sr中间合金对AZ91晶粒细化的研究

AZ91镁合金属于密排六方结构（HCP）,塑性较低,而采用晶粒细化的方法可在很大程度上改善镁合金的力学性能。采用Mg-8Sr中间合金作为AZ91镁合金的细化剂。试验结果表明,Mg-8Sr中间合金能起到很好的细化效果,并使AZ91镁合金的力学性能有很大的提高。     

稀土镧对Al-0.6Mg-0.7Si-0.2Mn汽车板材机械及腐蚀性能的影响

采用SEM、OM、拉伸试验（常温/高温）、弯曲试验和晶间腐蚀试验等测试方法,对添加不同含量稀土元素镧的Al-Mg-Si-Mn合金组织、机械性能及耐腐蚀性能等进行研究,分析稀土元素镧对合金机械和腐蚀性能的影响。结果表明,随La元素的添加,合金的铸态组织逐渐细化,第二相形貌得到了改善,同时减薄了该合金型材粗晶区厚度,提高了Al-Mg-Si-Mn合金的机械性能和耐腐蚀性能。当La添加量为0.2 wt.%时,晶粒细化效果最好,型材粗晶区最薄;La含量大于0.2 wt.%时,过量的La形成的初生相与合金晶粒细化剂中的Ti相互作用,减少了异质形核核心的数量,导致晶粒粗化现象,恶化合金的机械性能和耐腐蚀性能。     

添加Si粉对AZ91D镁合金激光表面改性

为提高镁合金的表面硬度,对预置Si粉的AZ91D进行高能CO2激光表面改性处理.采用光学显微镜、扫描电镜、电子探针微区分析和X射线衍射仪等方法研究了激光改性层的组织结构.结果表明:AZ91D表面改性层主要由α-Mg,Al12Mg17和Mg2Si组成.Si粉与镁合金完全发生反应形成金属间化合物Mg2Si,Mg2Si以树枝状分布.Al-Mn相由AZ91D基体中的团聚棒状变为激光改性层中的分散球状.激光表面改性后.由于Mg2Si相产生的强化和Mg17Al12产生的细晶强化,显微硬度从80 HV提高到324 HV.     

高锶含量AZ31镁合金的铸态组织及含锶相(英文)

研究不同Sr含量(0,0.3%,2.5%和5.0%,质量分数)的AZ31镁合金的铸态组织及含锶相。结果表明:在AZ31镁合金中添加Sr后,枝晶/晶粒尺寸变小,并且在0~5.0%的范围内,随着Sr含量的增加,枝晶细化且形态出现钝化现象,位于晶界/枝晶界的合金相分布更加弥散。添加0.3%Sr后,β-Mg17Al12相从未添加Sr的AZ31合金中的连续、不规则条状转变为不连续、不规则条状和/或细小颗粒状。在添加2.5%Sr和5.0%Sr的合金中发现了一些层片状共晶相,且后者的层片间距更加小。较高含量的Sr添加到AZ31镁合金中可以形成一种新的共晶和/或离异共晶三元Mg11Al5Zn4相,在添加2.5%Sr和5.0%Sr的合金中发现了Mg17Sr2相和Mg2Sr相。     

The synergistic ability of Al2O3 nanoparticles to enhance mechanical response of hybrid alloy AZ31/AZ91

AZ31/AZ91 hybrid alloy nanocomposite containing Al₂O₃ nanoparticle reinforcement was fabricated using solidification processing followed by hot extrusion. The nanocomposite exhibited similar grain size to the monolithic hybrid alloy, reasonable Al₂O₃ nanoparticle distribution, non-dominant (0 0 0 2) texture in the longitudinal direction, and 25% higher hardness than the monolithic hybrid alloy. Compared to the monolithic hybrid alloy (in tension), the nanocomposite synergistically exhibited higher 0.2%TYS, UTS, failure strain and work of fracture (WOF) (+12%, +7%, +99% and +108%, respectively). Compared to the monolithic hybrid alloy (in compression), the nanocomposite exhibited higher 0.2%CYS and UCS, and lower failure strain and WOF (+5%, +3%, −7% and −7%, respectively). The beneficial effects of Al₂O₃ nanoparticle addition on the enhancement of tensile and compressive properties of AZ31/AZ91 hybrid alloy are investigated in this paper.     

Ignition-proof performance and mechanism of AZ91D-3Nd-xDy magnesium alloys at high temperatures

This study focused on the synergistic effect of alloying elements neodymium(Nd) and dysprosium(Dy) on the ignition-proof performance of AZ91D alloy. The ignition-proof mechanism of AZ91D-3 Nd-x Dy(x = 0.5, 1.0, 1.5, 2.0 and 2.5 wt.%) alloy was discussed in depth through ignition-proof testing and microstructure observation. The results showed that the AZ91D-3 Nd-2 Dy alloy exhibited the highest ignition-point of 893 K, increased by 69 K as compared to the AZ91D alloy. The ignition-proof mechanism of Nd and Dy additions lay in three aspects:(1) the formation of denser oxide film consisting of Dy_2O_3 and MgO improves the oxidation resistance of the alloy,(2) the great reduction of the low melting-point phase β-Mg_(17)Al_(12), which leads to the decrease in the oxygen diffusion channels, and(3) the newly formed high melting-point phases(Al_2Nd and Al_2Dy), which block the oxygen diffusion channels and prevent the chemical reaction of Mg and oxygen.     

Microstructure refinement of AZ91D alloy solidified with pulsed magnetic field

The effects of pulsed magnetic field on the solidified microstructure of an AZ91D magnesium alloy were investigated. The experimental results show that the remarkable microstructural refinement is achieved when the pulsed magnetic field is applied in the solidification of AZ91D alloy. The average grain size of the as-cast microstructure of AZ91D alloy is refined to 104 μm. Besides the grain refinement, the morphology of the primary α-Mg is changed from dendritic to rosette, then to globular shape with changing the parameters of the pulsed magnetic field. The pulsed magnetic field causes melt convection during solidification, which makes the temperature of the whole melt homogenized, and produces an undercooling zone in front of the liquid/solid interface by the magnetic pressure, which makes the nucleation rate increased and big dendrites prohibited. In addition, primary α-Mg dendrites break into fine crystals, resulting in a refined solidification structure of the AZ91D alloy. The Joule heat effect induced in the melt also strengthens the grain refinement effect and spheroidization of dendrite arms.     

浇注温度和细化剂对半固态A356合金组织的影响

采用低温铸造和晶粒细化复合工艺制备A356合金半固态坯料,研究了浇注温度和细化剂(Al-5Ti-1B)添加量对半固态坯料组织的影响。结果表明,随着浇注温度从715℃降到635℃,α-Al晶粒形貌从树枝晶向蔷薇状形态再到等轴晶组织变化,浇注温度越低,晶粒越细小圆整。当浇注温度降到615℃时,晶粒开始出现粗化和不均匀。在相同温度下,随着晶粒细化剂添加量的增加,晶粒更加细小,但细化效果随着添加量的增加变得不明显。当浇注温度低于635℃时添加细化剂,晶粒尺寸和形貌无明显变化。低过热度浇注和晶粒细化复合工艺制备A356合金半固态坯料的最佳工艺条件是:浇注温度为635~655℃,细化剂添加量为0.1%~0.2%。     

Grain refinement of Al-3.5FeNb-1.5C master alloy on pure Al and Al-9.8Si-3.4Cu alloy

The refinement potential of Al-3.5 Fe Nb-1.5 C master alloy on pure aluminium and Al-9.8 Si-3.4 Cu alloy has been investigated. Different amounts of Al-3.5 Fe Nb-1.5 C master alloy were added to estimate the optimal addition level. It was found that the addition of Al-3.5 Fe Nb-1.5 C grain refiner can promote significantly the refinement of grains in the pure aluminium, particularly at 0.1 wt.%, with the mean primary aluminium α-grain size reducing to 187±3 μm from about 1-3 mm. Similarly, the microstructural study of the Al-9.8 Si-3.4 Cu alloy die casting at different weight percentages(viz. 0.0 wt.%, 0.1 wt.% and 1.0 wt.%) of Al-3.5 Fe Nb-1.5 C master alloy shows that the Al-3.5 Fe Nb-1.5 C master alloy as a grain refiner is also acceptable for Al-Si cast alloys when the silicon content is more than 4 wt.%. As a result of inoculation with Al-3.5 Fe Nb-1.5 C master alloy, the average grain size of α-Al is reduced to 22±3 μm from about 71±3 μm and grain refining efficiency is not characterized by any visible poisoning effect, which is the major limitation in the grain refinement of Al-Si cast alloys by applying Al-Ti-B ternary master alloys. Mechanical properties such as ultimate tensile strength and yield strength are significantly improved by 9.6% and 9.7%, respectively.     

熔体处理对A357合金枝晶搭接点的影响

采用双热电偶法分别测得不同熔体处理A357合金的枝晶搭接点，进而通过热分析法分别计算出枝晶搭接点的固相体积分数fs^coh。结果表明，冷却速率和晶粒细化处理对fs^coh的增大有较大影响；而变质剂（Sr）对fs^coh值的影响不明显。分析表明，冷却速率的提高以及晶粒细化剂的加入细化了晶粒和延缓枝晶的生长，从而提高fs^coh，而Sr的加入只改变Si的形态，对fs^coh的影响不大。     

Microstructure and mechanical properties of AZ91 magnesium alloy with minor additions of Sm,Si and Ca elements

The effects of Sm, Si and Ca on the microstructure and mechanical property of AZ91 magnesium alloy were investigated by means of optical microscopy(OM), differential scanning calorimetry(DSC), scanning electronic microscopy(SEM), X-ray diffraction(XRD) and tensile testing. The results indicated that the addition of 1.5 wt.% Sm with or without 0.8 Si/Ca led to a decrease in the volume fraction of the β-Mg17 Al12 phase and the formation of the intermetallic compounds of Al-Sm, Mg2 Si, Mg Al Ca and Al2 Ca. The microstructure of AZ91 alloy was significantly refined and distribution became discrete with additions of Sm and Ca; the average grain size of the α-Mg matrix was reduced from 239.7 ± 16.9 μm to 66.34 ± 5.10 μm. The AZ91-Sm-Ca alloy exhibited a good combination of yield strength at 135 MPa, ultimate tensile strength at 199 MPa and elongation at 4.32%, which was ascribed to grain refinement strengthening. Furthermore, the T6 treated AZ91-Sm-Ca alloy possessed yield strength of 154 MPa and elongation of 7.1%, which was due to grain refinement strengthening and reduction in discontinuous precipitates.     

La对Fe-36Ni低膨胀合金凝固组织的影响

研究了La对Fe-36Ni低膨胀合金凝固组织的影响.结果表明,加La处理后,合金的凝固组织得到显著改善,随着合金中La含量的增加,凝固组织的等轴晶比例增加,等轴晶尺寸减小,树枝晶变细变短,一次枝晶间距减小,二次枝晶间距基本不变.经La处理后,Fe-36Ni低膨胀合金中形成了大量高熔点的La2O2S颗粒,尺寸约为4μm.错配度计算表明,Fe-36Ni低膨胀合金的低指数面与La2O2S的低指数面有5.42％的较低错配度,因此La2O2S可以作为有效的非均质形核的核心,提高形核率,细化合金的凝固组织.