Ca对碳质孕育含Fe的Mg-3%Al合金晶粒细化的“免毒化”作用(英文)

利用Ca和碳质孕育对Mg3%Al合金进行复合变质处理,并研究了Fe及其Fe的添加顺序对细化效果的影响。与碳质孕育相比,Ca和碳复合孕育后的晶粒细化效果更为显著,Fe及其添加顺序对复合孕育细化效果无显著影响。Ca的添加可有效避免碳质孕育MgAl合金中因Fe所导致的晶粒粗化作用。在Ca和碳质复合孕育试样中可观察到大量的AlCO颗粒,这些颗粒实际应为Al4C3,并作为α-Mg的形核核心。然而,在熔体中添加Fe后,试样中可观察到大量在AlFe或AlCFe表面吸附Al4C3的双相粒子,该双相粒子可作为α-Mg的形核核心并导致晶粒细化。Ca有利于该双相粒子的生存,并与工艺条件无关,从而使得Fe对晶粒细化的"毒化"作用得到有效抑制,即Ca对Fe有"免毒化"效果。     

Fe对Mg-3Al合金碳质孕育晶粒细化的影响

在本能晶粒细化基础上,向高纯Mg-3Al合金熔体中添加Fe元素,对粗化后的晶粒进行碳质孕育法晶粒细化处理,研究了合金凝固后的晶粒尺寸变化,并对Fe的影响机理进行分析与讨论。结果表明,随着Fe含量的增加,Mg-3Al合金的凝固晶粒尺寸呈先增大后减小的趋势;此外,Fe含量较低时,碳质孕育法处理能获得明显的晶粒细化效果,但随着Fe含量的增加,碳质孕育法细化效果逐渐衰弱,直至完全消失。分析表明,合金晶粒尺寸的变化与凝固过程中的晶核性质变化相关。     

Fe对Mg-9Al合金碳质孕育晶粒细化效果的影响

向高纯Mg-9Al合金熔体中添加不同含量的Fe,研究合金凝固晶粒尺寸变化,在此基础上对熔体进行碳质孕育晶粒细化处理,研究Fe对碳质孕育细化效果的影响,并对Fe的影响机理进行分析与讨论。结果表明,微量Fe的引入会导致合金晶粒尺寸迅速增加,但当Fe含量达到一定程度时,合金晶粒又能被再次细化;此外,当Fe含量较低时,碳质孕育处理能收获一定的晶粒细化效果,但随着Fe含量的增加,碳质孕育细化效果逐渐衰弱。分析表明,合金晶粒尺寸的变化与Fe能影响熔体中的晶核性质有关。     

Fe元素对Mg-3Al合金的晶粒细化与机理

将无水FeCl3直接添加到Mg-3Al合金熔体中进行孕育处理,研究了Fe元素对合金的晶粒细化现象和机理。结果表明,高纯Mg-3Al合金存在"本能晶粒细化"现象,当引入Fe元素时,微量的Fe可引起合金晶粒的明显粗化,但当Fe元素含量较高时,Fe的存在又能引起合金晶粒的再次细化。分析表明,Fe元素能够与高纯熔体中的含碳晶核相互作用,降低晶核的形核能力,这是Fe元素引起合金晶粒粗化的主要原因,但之后的晶粒细化现象与Al-Fe颗粒的析出无关,而更可能是形核能力已降低的形核相随着Fe含量的增加其点阵结构和参数再次发生了明显的改变,并再次成为合金凝固时的主要晶核。     

利用热分析技术评估碳质孕育Mg-3%Al合金熔体的凝固特性（英文）

将Mg-3%Al合金熔体进行碳质孕育处理并保温不同时间,评估保温时间对孕育细化效果的影响。利用计算机辅助热分析技术对经碳质孕育并保温不同时间合金熔体的凝固特性进行分析。结果表明:碳质孕育能显著细化Mg-3%Al合金。当保温时间延长至60 min时孕育衰退不明显。碳质孕育能明显改变合金熔体的冷却曲线,孕育处理后初始形核温度和最低形核温度升高,再辉过冷度和再辉时间几乎降低至0。碳质孕育的晶粒细化效果能通过冷却曲线形状和凝固特征参数进行评估,包括初始形核温度、最低形核温度、再辉过冷度和再辉时间。     

Al4 C3细化AZ91合金晶粒的现象和机理

通过向熔体中直接添加Al4C3颗粒,研究了Al4C3对AZ91合金的晶粒细化现象和机理的影响.结果表明,Al4C3颗粒对AZ91合金的晶粒细化效果与孕育参数直接相关,孕育温度越高孕育时间越久,Al4C3的细化效果越明显.研究发现,实验添加的Al4C3颗粒并没有直接成为镁的晶核,而是被推开到了晶粒生长界面前沿,Al4C3的细化作用主要是因为Al4C3发生了微量的溶解,从而向熔体中提供了碳,碳的存在对熔体起到了碳质孕育法处理的作用.     

汽车发动机阀盖用Mg-Gd合金的合金化效应研究

采用Al合金化的方法制备了汽车发动机阀盖用Mg-Gd-Al合金,研究了Al含量对Mg-Gd合金晶粒细化、物相组成、有效形核颗粒数量密度和尺寸分布的影响。结果表明,添加0.8%~1.3%Al可以对Mg-Gd合金起到明显的晶粒细化作用;当添加Al元素后,合金中除了α-Mg基体和Mg5Gd相外,还出现了Al2Gd和(Mg,Al)3Gd相;随着合金中Al含量的增加,Mg-Gd合金中有效形核颗粒的数量密度逐渐增加,且有效形核颗粒的尺寸有所增大。     

Mg-Al-Nd/Sr耐热镁合金的组织结构与蠕变性能

以Mg-6Al合金为基体,分别单一添加稀土Nd、Sr和复合添加稀土Nd和碱土Sr元素,采用水冷模工艺制备Mg-6Al-6Nd,Mg-6Al-2Sr和Mg-6Al-2Sr-2Nd耐热镁合金,并比较研究单一添加Nd或Sr和复合添加稀土Nd和碱土Sr对合金组织结构和蠕变性能的影响。结果表明:复合添加稀土Nd和碱土Sr后,合金中除了析出第二相Al2Nd、Al11Nd3和Al4Sr外,还析出Sr和Nd相互取代的Al4(Sr,Nd)和Al11(Nd,Sr)3复合相;在Mg-6Al-2Sr基础上添加2%Nd,不仅细化合金枝晶间距,还显著地提高第二相的分布密度,增强合金蠕变过程中位错与第二相交互作用,提高合金的蠕变性能。     

Sb、Y、Nd元素对Mg-6%Al合金显微组织的影响

本文主要研究了Sb、Y和Nd元素复合添加时对Mg-6%Al合金铸态组织的影响.研究结果表明,Sb、Y和Nd元素对Mg-6%Al合金组织均有细化作用,当元素复合添加0.5%Y 1.0%Nd时,晶粒平均直径由102.04μm细化至57.47 μm,细化效果最为显著.经测试分析,Sb、Y、Nd与合金中镁铝元素形成热稳定性较高的金属间化合物Mg3Sb2、Al2Y和Al2Nd,各相在α-Mg晶粒内和晶界均有分布,在凝固期间,首先析出并成为α-Mg的异质核心,细化了合金的铸态组织.     

Fabrication of a New Mg-50%Al4C3-6%Ce Master Alloy and Its Refinement Mechanism on AZ91D Alloy

采用粉末原位合成工艺成功制备新型Mg-50%Al4C3-6%Ce中间合金,并利用X射线衍射(XRD)仪、扫描电镜(SEM)及能谱(EDS)分析对其进行物相鉴别和形貌分析。结果显示,中间合金主要由层片状Al4C3和细杆状Al4Ce以及Mg基体组成。在AZ91D镁合金熔体中加入Mg-50%Al4C3-6%Ce中间合金可明显细化枝晶组织,枝晶形貌由六重对称的树枝状演变为花瓣状,当加入量为1.2%(质量分数)时,平均晶粒尺寸由基体合金的360μm降至65μm。晶粒细化机制可归结为Al4C3颗粒作为初生α-Mg的异质晶核,Ce富集于固液界面,引起成分过冷,从而激活固液界面前沿潜在的Al4C3核心,提高Al4C3的形核率。     

Assessment of solidification characteristics of carbon-inoculated Mg-3%Al melt by thermal analysis

The Mg-3%Al melt was inoculated by carbon with different holding time. The effect of holding time on grain refining efficiency was evaluated. The solidification characteristics of the carbon-inoculated Mg-3%Al melt with different holding time were assessed by computer-aided cooling curve analysis. The results showed that Mg-3%Al alloy could be effectively refined by carbon inoculation. Slight fading phenomenon occurred with increasing the holding time to 60 min. Carbon inoculation could significantly influence the shape of cooling curves of Mg-3%Al melt. The nucleation starting and minimum temperatures increased. The recalescence undercooling and duration decreased to almost zero after carbon inoculation. The grain refining efficiency of carbon inoculation could be assessed by the shape of the cooling curve and solidification characteristic parameters including nucleation starting and minimum temperatures, recalescence undercooling and duration.     

Effect of strontium on the grain refining efficiency of Mg–3Al alloy refined by carbon inoculation

The effect of Sr on the grain refining efficiency of the Mg–3Al alloy refined by carbon inoculation has been investigated in the present study. A significant grain refinement was obtained for the Mg–3Al alloy treated with either 0.2% C or 0.2% Sr. The Al–C–O particles were found in the sample refined by 0.2% C, and the element O should come from reaction between Al₄C₃ nuclei of Mg grains and water during the process of sample preparation. The grain size of the sample refined by carbon inoculation was further decreased after the combined addition of Sr. The grain size decreased with increasing Sr content. Much higher refining efficiency was obtained when the Sr addition was increased to 0.5%. Sr is an effective element to improve the grain refining efficiency for the Mg–Al alloys refined by carbon inoculation. The number of Al₄C₃ particles in the sample refined by the combination of carbon and Sr was more than that in the sample refined by only carbon. No Al–C–O–Sr-rich particles were obviously found in the sample refined by the combination of carbon and a little (<0.5%) Sr addition.     

镁合金铸态晶粒细化技术的研究进展

综述了熔体过热法、氯化铁法、碳质材料变质处理法、熔体搅拌法以及加Zr、Ca或Sr等镁合金铸态晶粒细化技术的研究现状和最新进展,重点分析了不同细化方法的工艺特点和细化机理,指出了镁合金铸态晶粒细化研究还存在的问题,并对今后的发展方向进行了展望.     

Effect of limestone ores on grain refinement of as-cast commercial AZ31 magnesium alloys

The grain refinement of the as-cast AZ31 alloys by limestone particles was investigated by grain refining tests and microstructure observations. The results show that the limestone particles have a good grain refining potency, which is deeply related to the addition level of limestone and melting temperature. The optimal addition level and melting temperature are 2.0% (mass fraction) and 720 °C, respectively. The average grain size of AZ31 alloy is reduced from (556±60) to (236±22) μm. The sound grain refining by raw limestone particles has a good anti-fading capacity without any significant grain coarsening in a 40 min holding time. The concerned grain refining mechanism should be attributed to the inoculated Al-C and Al-C/Al-Mn-(Fe) nuclei. Ultrasonic treatment can enhance the grain refining efficiency of limestone particles through cavitation-enhanced nucleation mechanism.     

Response of an Al—Cr alloy towards grain refinement by Al—5Ti-1B master alloy

Grain refining of an Al–2%Cr alloy by Al–5Ti-1B master alloy (5/1 TiBAl) has been studied as a function of the addition rate of the grain refiner in the range 0.2–1.2% and holding times up to 120 minutes. This study revealed that an effective grain refinement of Al–2%Cr requires a minimum addition of 1.2% grain refiner as against the 0.2% which is normally required for most of the conventional Al alloys. The work further revealed that the effect of grain refiner starts fading after holding the melt for about 5 minutes, irrespective of the addition rate of grain refiner. The formation of complex aluminides in the presence of Cr seems to be the primary reason for the poor grain refining response of this alloy at low addition rates of grain refiner. At high addition rates, the better grain refining behaviour of the present alloy was found to be essentially due to the availability of finer unreacted nucleating sites (TiAl₃ and TiB₂).     

Processing Effects on Grain Refinement of AZ31 Magnesium Alloy Treated with a Commercial Al-10Sr Master Alloy

The effects of Sr amount and melt holding time on the grain refinement of AZ31 magnesium alloy treated with a commercial Al-10Sr master alloy are investigated. The effects of solutionizing, rolling, and remelting of commercial Al-10Sr master alloy on the grain refinement of AZ31 magnesium alloy are also investigated. An increase in Sr amount from 0.01 to 0.1 wt.% or melt holding time from 20 to 80 min causes the grain size of AZ31 alloy treated with the commercial Al-10Sr master alloy to gradually decrease. In addition, the solutionizing, rolling, or remelting of commercial Al-10Sr master alloy can improve the refinement efficiency of the master alloy to AZ31 alloy, and the improvement resulting from the remelting is best obvious, followed by rolling and solutionizing, respectively.     

铸铁孕育机制

铸铁孕育技术的应用已逾六十年,至今对孕育的机理仍不很清楚。争议的焦点在于,究竟是孕育提供了石墨形核的异质基底;抑或激发了石墨自身形核。当前大多数人持前一观点。以往的工作对孕育铁水中碳分布的实验研究较欠缺。由于对孕育过程中的碳分布图像了解不够,必然影响了对孕育本质的认识。本文从微观和统计的角度对孕育样品中碳的浓度和活度分布的特点进行了测定,在此基础上探讨了孕育机理。     

Al-Zn-Mg-Cu-Zr-Sc合金铸态Al3(Sc，Zr)相形貌的研究

采用金相显微镜、扫描电镜和能谱分析,研究Sc细化Al-Zn-Mg-Cu-Zr合金铸态组织的机制和一次Al3(Sc,Zr)粒子的形貌特征。结果表明:从熔体中析出的Al3(Sc,Zr)一次粒子是α(Al)固溶体的有效形核剂,该粒子以亚稳的L12型Al3Zr为核心,形成富钪与富锆Al3(Sc,Zr)层相间排列的多层复合结构。在Al-9.0Zn-2.5Mg-2.5Cu-0.15Zr合金中添加0.20%～0.60%(质量分数)的钪,合金的铸态组织由粗大的树枝晶变为等轴晶,随着钪含量的增加,合金铸态组织得到进一步细化。     

Grain refinement of Mg-Al binary alloys inoculated by in-situ oxidation

Utilizing oxide inclusion to induce heterogeneous nucleation event is an available method to achieve grain refinement. In this study, Mg-Al binary alloys were refined by inoculation of in-situ oxidation process. Results show that MgO and MgAl₂O₄ phases are primary oxide products for Mg-xAl alloys inoculated by in-situ oxidation. For pure Mg and Mg-1Al alloy, MgO is the only oxide product. MgAl₂O₄ is another oxide product for Mg-xAl alloy as Al content increases to 3 wt.%. For Mg-3Al alloy, average grain size significantly decreases from 1135 to 237 μm, with a high grain refining ratio of 79.1%. Both MgO and MgAl₂O₄ possess nucleating potency for α-Mg grain. MgAl₂O₄ exhibits a higher nucleating potency due to the lower misfit with α-Mg. The grain refinement of Mg-xAl alloys inoculated by in-situ oxidation process is attributed to heterogeneous nucleation events of α-Mg grains on MgO or MgAl₂O₄ particles.