Mg-Si合金系B81-型合金基因浓度及性质的研究

以Mg-Si合金系为例,根据合金基因理论和中心配位原子模型,推导密排六方(HCP)结构B8_(1)-型合金基因浓度的表达式。计算B8_(1)-型有序合金的基因浓度随Si的原子数分数(xSi)和有序度(σ)的变化,阐明B8_(1)-型有序合金的基因浓度随xSi和σ的变化特征。计算B8_(1)-型有序合金和无序Mg((1-x))Six合金随xSi的变化特征。研究结果表明:与无序合金相比,B8_(1)-型有序合金的参数如结合能等变化更大,因此,有序化可提高Mg-Si合金的抗压强度;s和p轨道上的共价电子数(分别为ns和np)随Si的原子数分数的增加而增多,当xSi>0.4时反而减少;共价电子数增多有利于提高Mg-Si合金的抗腐蚀强度,这为智能化制备高强轻质Mg合金指明了方向。

稀土Ce对过共晶Mg-Si合金中初生Mg_2Si相变质的影响

利用Mg-20%(质量分数,下同)Ce中间合金对过共晶Mg-Si合金进行变质处理,研究了Ce加入量对该合金中初生Mg2Si相变质效果(主要是形态)的影响规律,并讨论其变质机制。研究结果表明:当加入量达到并超过0.4%以后,稀土Ce可有效变质过共晶Mg-Si合金中的初生Mg2Si相,其形态由粗大树枝晶转变为具有非规则外形的颗粒,且随Ce加入量增加到2.0%,Ce对初生Mg2Si相的变质均未产生明显的过变质现象。变质机理应主要与稀土元素富集于Mg2Si相生长表面并抑制优先生长晶向的生长有关。

Sr对过共晶Mg-Si合金中初生Mg_2Si相变质的影响

利用Mg-20%Sr中间合金对过共晶Mg-Si合金进行变质处理,对比研究了碱土元素Sr加入量对Mg2Si初晶变质效果(主要包括形态和尺寸)的影响规律,并讨论其变质机制。研究结果表明:碱土元素Sr对过共晶Mg-Si合金中的Mg2Si初晶可有效变质。随着Sr含量的增加,Mg2Si初晶的平均尺寸和尺寸分布范围均逐渐降低,其形态由粗大树枝状晶、细小树枝晶、非规则外形颗粒到规则外形颗粒逐渐过渡。当Sr含量达到2.0%,此时Mg2Si初晶主要呈现为规则外形,平均尺寸为50μm左右。其变质机理应主要与碱土元素富集于Mg2Si相生长表面并抑制优先生长晶向的生长有关。

Ca对过共晶Mg-Si合金中初生Mg_2Si相变质的影响

利用Mg-20%Ca中间合金对过共晶Mg-Si合金材料进行变质处理,研究了Ca加入量对Mg2Si初晶变质效果的影响规律,并讨论其变质机理。研究结果表明:Ca可有效变质过共晶Mg-Si合金中的Mg2Si初晶。随着Ca含量的增加,Mg2Si初晶形态由粗大树枝状晶、细小树枝晶、非规则外形颗粒到规则外形逐渐过渡。当Ca百分含量达到1.2%时,Mg2Si初晶主要呈现为规则外形。其变质机理应主要与碱土金属富集于Mg2Si相生长表面并抑制优先生长晶向有关。

石英原位自生制备Mg_2Si增强Mg-Si合金及其显微组织

采用石英粉和石英砂与纯镁原位反应自生获得Mg2Si相,在不同温度下浇铸制备高Si含量的Mg-Si二元合金,分析原位反应的热力学条件、合金的凝固过程、组织形态及分布。结果表明,在实验条件下石英与纯镁原位自生反应可以自发进行,随着Si含量的提高,合金中的Mg2Si相以汉字状、枝晶状及初生块状形态。采用石英粉更易于原位自生获得Mg2Si相,浇注温度越高Mg2Si相分布越均匀。

Sr对过共晶Mg-Si合金微观组织的影响

利用Mg-25%Sr中间合金对过共晶Mg-Si合金进行变质处理,研究碱土元素Sr对Mg2Si初晶的变质效果(主要包括形态和尺寸),并讨论其变质机理。研究结果表明:碱土元素Sr对过共晶Mg-Si合金中的Mg2Si初晶可有效变质。初生Mg2Si的尺寸明显降低(平均尺寸由50μm左右降低为20μm左右),其形态由粗大树枝状晶、非规则外形颗粒变化为外形相对规则颗粒。共晶Mg2Si由明显的汉字状变化为呈细短的棒状。其变质机理主要有两点:一是Sr的富集颗粒作为异质形核点诱导更多的初生Mg2Si生长;二是Sr富集于共晶Mg2Si相生长表面,抑制其优先生长晶向的生长。

Zn对生物医用Mg-Si合金组织与力学性能的影响

在生物医用Mg-1.38Si合金中加入Zn,研究Zn添加量对合金凝固组织和力学性能的影响。结果表明,Zn对合金中的Mg_(2)Si相具有较好的变质效果。添加Zn后,合金中的初生Mg_(2)Si相由多边形状转变为尺寸更为细小的颗粒状。随着Zn含量的增加,共晶Mg_(2)Si相逐渐细化。添加Zn能够改善Mg-1.38Si合金的力学性能。随着Zn含量的增加,合金的室温抗拉强度、伸长率、压缩断裂强度、塑性变形量均逐渐提高。

熔盐电沉积法制备Mg-Si中间合金的研究

在以CaCl_2-CaF_2为熔盐体系、CaO-SiO_2为原料、石墨坩埚为阳极、液态镁液为阴极的电解槽中采用电沉积法制备Mg-Si中间合金,探究了温度、电流强度和电解时间对镁硅合金制备过程中反电动势和电流效率的影响。结果表明,反电动势随电流强度的增加而升高;当温度从860℃升高到960℃时,反电动势由1.97 V降低至1.78 V;加入2%CaO-SiO_2可使反电动势平均降低0.26 V;加料周期是48 min;电流效率、硅含量随电流的增大先升高再降低,最佳电解时间是120 min;合金中硅的分布较均匀,无明显偏析。

稀土Er和Ce复合改性对过共晶Mg-Si合金组织与性能的影响

通过金相、SEM、EDS和XRD等方法研究了稀土元素Er、Ce复合改性对过共晶Mg-3.2Si合金中初生Mg_2Si相的影响,并探讨了改性机制。结果表明,在过共晶Mg-3.2Si合金中,添加约0.6%(质量比,下同)Er时,初生Mg_2Si相的平均尺寸由150μm减小到40μm,其形态从粗大树枝状变为不规则多面体;在此基础上,继续添加1.0%Ce,可获得5~10μm大小的多面体或球状初生Mg_2Si相,改性效果最佳;但稀土添加过量,会出现过改性现象。改性机制:稀土Er和Ce吸附或富集在初生Mg_2Si相表面,降低固液界面张力,减小临界形核功,有利于更多初生Mg_2Si晶核的生成;稀土Er和Ce在初生Mg_2Si相的表面富集,减小了晶向之间的相对生长速度,使初生Mg_2Si相从粗大树枝状变为不规则多面体形状;合金凝固时,稀土Er与Ce的晶体结构相同,形成了连续固溶体。当稀土添加量为0.6%Er和1.0%Ce时,Mg-3.2Si合金试样的抗拉强度σb与伸长率δ分别提高到127 MPa和3.7%最大值。

Zn对Mg-Si合金组织与生物腐蚀行为的影响

研究了Zn对Mg-1.38Si合金凝固组织和生物腐蚀行为的影响。结果表明,Zn对合金中的MgSi相具有较好的变质作用。添加Zn后,多边形状的初生MgSi相转变为尺寸更为细小的颗粒状,同时,共晶MgSi相也得到细化。随着Zn含量增加,合金中MgSi相的数量逐渐降低,试样在SBF溶液中的腐蚀速率和自腐蚀电流密度均逐渐降低,自腐蚀电位也逐渐向正向移动,表明合金的耐腐蚀性能逐渐提高。Zn添加量为1.5%时,合金的耐腐蚀性能最佳。

均匀化对Al-Mg-Si-Cu合金组织和性能的影响

采用拉伸力学性能测试、金相观察、扫描电镜(SEM)、透射电镜(TEM)和能谱分析(EDS)研究了均匀化温度和时间及Mn含量对新型Al-Mg-Si-Cu合金微观组织和力学性能的影响。结果表明,均匀化温度的升高和Mn含量的增加均加快β-AlFeSi相向α-AlFeSi相的转变,α-AlFeSi相的数量随均匀化时间的延长而增加,但这一过程取决于合金中的Mn含量,仅依靠均匀化处理而不加入微量Mn,不能获得适宜形态的α-AlFeSi相颗粒。均匀化处理后,在空冷过程中析出粗大棒状Mg2Si(β')相,急冷后没有观察到此相。合金的拉伸强度降低,但急冷降低的程度要小于空冷。

Mn对Al-Mg-Si-Cu铝合金车身板组织和性能的影响

通过拉伸和埃里克森实验以及扫描电镜/能谱、透射电镜和金相分析,研究Mn的质量分数对Al Mg Si Cu铝合金汽车板显微组织、力学性能和成形性的影响·研究表明,随Mn质量分数增加,Al Mg Si Cu汽车板铝合金不可溶结晶相及弥散相粒子数量均增加,不可溶结晶相使合金组织纤维化对板材冲压成形性不利,弥散相粒子阻碍再结晶晶粒长大;提高Mn的质量分数,Al Mg Si Cu汽车板铝合金的强度增加,但延伸率和冲压成形性降低·

Sb对过共晶Mg-4.8%Si合金中Mg_2Si初晶变质的影响

利用Mg-20%Sb中间合金对过共晶Mg-4.8%Si合金进行变质处理,考察Sb的含量对Mg2Si初晶变质效果(主要包括形态和尺寸)的影响规律,并讨论其变质机制。结果表明:Sb的加入量是决定其能否有效变质过共晶Mg-4.8%Si合金中Mg2Si初晶的重要因素;在未变质的过共晶Mg-Si合金中,Mg2Si初晶以粗大的树枝晶状为主;当Sb加入量低于0.8%(质量分数)时,Mg2Si初晶形态无明显改善,其平均尺寸略有降低;当Sb加入量达到并超过1.2%后,Sb才能有效变质过共晶Mg-4.8%Si合金中Mg2Si初晶,且Mg2Si初晶呈细小的颗粒状弥散分布,其平均尺寸迅速减小;其变质机制应与残留在熔体中弥散分布的Mg3Sb2粒子作为Mg2Si初晶的形核核心有关。

Corrosion mechanism associated with Mg_2Si and Si particles in Al-Mg-Si alloys

The electrochemical behaviors and coupling behaviors of the Mg2Si and Si phases with α（Al） were investigated, the corrosion morphologies of Al alloys containing Mg2Si and Si particles were observed, and the corrosion mechanism associated with them in Al-Mg-Si alloys was advanced. The results show that Si particle is always cathodic to the alloy base, Mg2Si is anodic to the alloy base and corrosion occurs on its surface at the beginning. However, during its corrosion process, the preferential dissolution of Mg and the enrichment of Si make Mg2Si transform to cathode from anode, leading to the anodic dissolution and corrosion of the alloy base at its adjacent periphery at a later stage. As the mole ratio of Mg to Si in an Al-Mg-Si alloy is less than 1.73, it contains Mg2Si and Si particles simultaneously in the grain boundary area, and corrosion initiates on the Mg2Si surface and the precipitate-free zone （PFZ） at the adjacent periphery of Si particle. As corrosion time is extended, Si particle leads to severe anodic dissolution and corrosion of the PFZ at its adjacent periphery, expedites the polarity transformation between Mg2Si and the PFZ and accelerates the corrosion of PFZ at the adjacent periphery of Mg2Si particle.

Modification of Mg_2Si in Mg-Si alloys with neodymium

The modification effect of neodymium （Nd） on Mg2Si in the hypereutectic Mg-3%Si （mass fraction） alloy was investigated by optical microcopy, scanning electron microscopy and X-ray diffraction. The results indicate that the morphology of the primary Mg2Si transforms from coarse dendrite into fine polygon with increasing Nd content. The average size of the primary Mg2Si significantly decreases to about 10 ~ma with increasing Nd content up to 1.0%, and then becomes coarser again. The modification and refinement of the primary Mg2Si are mainly attributed to the poisoning effect. The NdMg2 phase in the primary Mg2Si transforms into NdSi and NdSi2 compounds as the Nd content exceeds 3.0%. Therefore, it is reasonable to conclude that the proper Nd （1.0%） addition can effectively modify and refine the primary Mg2Si.

Effect of minor Zr and Sc on microstructures and mechanical properties of Al-Mg-Si-Cu-Cr-V alloys

The effects of minor contents of Zr and Sc on the microstructures and mechanical properties of Al-Mg-Si-Cu-Cr-V alloy were studied. The results show that the effects of minor Zr and Sc on the as-cast grain refinement in the ingots, the improvement in the strength of the as-extruded alloys and the restriction of high angle grain boundaries in the aged alloys can be sorted as Al3ScAl3 （Zr,Sc）Al3Zr. None of them could stop the nucleation of recrystallization, but Al3 （Zr,Sc） phase is a more effective inhibitor of dislocation movement compared to Al3 Sc in the aged alloys. Compared with the mechanical properties of the aged alloy added only 0.15% Sc, the joint addition of Zr and Sc to the alloy leads to a very slight decrease in strength with even no cost of ductility. Taking both the production cost and the little bad influence on mechanical properties into consideration, an optimal content of Zr and Sc in the Al-Mg-Si-Cu-Cr-V alloy to substitute 0.15% Sc is 0.13% Zr＋0.03% Sc.

Effects of high temperature pre-straining on natural aging and bake hardening response of Al-Mg-Si alloys

The influences of high temperature pre-straining (HT-PS) on the natural aging and bake hardening of Al?Mg?Si alloys were investigated by Vickers microhardness measurements, differential scanning calorimetry (DSC) analysis and transmission electron microscopy (TEM) characterization. The results show that pre-straining at 170 °C immediately after quenching can effectively resolve the rather high T4 temper hardness caused by the conventional room temperature (RT) pre-straining treatment, and give a better bake hardening response (BHR) after paint-bake cycle. HT-PS 7% at 170 °C for 10 min is chosen as the optimum process as it provides lower T4 temper hardness and better BHR. The simultaneous introduction of dislocations and Cluster (2) can significantly suppress the natural aging and promote the precipitation of β″ phase, and reduce the effects of deformation hardening by dynamic recovery.

Influence of thermomechanical processing on microstructure,texture evolution and mechanical properties of Al-Mg-Si-Cu alloy sheets

Influence of thermomechanical processing on the microstructure, texture evolution and mechanical properties of A1-Mg-Si-Cu alloy sheets was studied systematically. The quite weak mechanical properties anisotropy was obtained in the alloy sheet through thermomechanical processing optimizing. The highly elongated microstmcture is the main structure for the hot or cold-rolled alloy sheets. H {001 } （110） and E { 111 } （110） are the main texture components in the surface layer of hot-rolled sheet, while ]/-fibre is dominant in quarter and center layers. Compared with the hot-rolled sheet, the intensities offl-fibre components are higher after the first cold rolling, but H {001 }（110） component in the surface layer decreases greatly. Almost no deformation texatre can be observed after intermediate annealing. And fl-fibre becomes the main texture again after the final cold rolling. With the reduction of the thickness, the through-thickness texture gradients become much weaker. The through-thickness recrystallization texture in the solution treated sample only has cubeyD {001 }（310） component. The relationship among thermomechanical processing, microstructure, texture and mechanical orouerties was analyzed.

Crack elimination and strength enhancement mechanisms of selective laser melted Si-modified Al−Mn−Mg−Er−Zr alloy

In order to increase the processability and process window of the selective laser melting(SLM)-fabricated Al−Mn−Mg−Er−Zr alloy,a novel Si-modified Al−Mn−Mg−Er−Zr alloy was designed.The effect of Si alloying on the surface quality,processability,microstructure,and mechanical properties of the SLM-fabricated alloy was studied.The results showed that introducing Si into the Al−Mn−Mg−Er−Zr alloy prevented balling and keyhole formation,refined the grain size,and reduced the solidification temperature,which eliminated cracks and increased the processability and process window of the alloy.The maximum relative density of the SLM-fabricated Si/Al−Mn−Mg−Er−Zr alloy reached 99.6%.The yield strength and ultimate tensile strength of the alloy were(371±7)MPa and(518±6)MPa,respectively.These values were higher than those of the SLM-fabricated Al−Mn−Mg−Er−Zr and other Sc-free Al−Mg-based alloys.

Effect of copper on precipitation and baking hardening behavior of Al-Mg-Si alloys

The effects of copper on the ageing precipitation behavior of as-quenched and pre-aged AA6016 aluminum alloy were studied by differential scanning calorimetry （DSC）, Vickers hardness measurement and transmission electronic microscopy （TEM）. The results indicate that the addition of copper facilitates the growth of clusters （GP I） to the critical size during pre-ageing. Therefore, the addition of copper accelerates the transition from GP I （pre-β＂） to GP II （β＂） during final artificial ageing, and finally results in the favorable paint-bake response. However, the one with the copper level of 0.3% does not show significant baking hardening response as expected. Pre-aging can also reduce the detrimental effect due to natural aging of copper-containing alloys.