镁对过共晶铝铁合金组织形貌的影响1.doc

镁对过共晶铝铁合金组织形貌的影响 王正军 刘莲香 摘 要 针对普通熔铸条件下过共晶Al-Fe合金初生富铁相严重割裂基体、恶化合金性能的问题，采用元素Mg对过共晶Al- 5%Fe合金进行变质细化处理，Mg以Al-10%Mg中间合金形式加入。借助光学显微镜等分析了Al-10%Mg中间合金晶粒细化剂加入量和熔体保温时间对过共晶Al-5%Fe合金微观组织形貌及性能的影响。试验表明：在过共晶Al-5%Fe合金中加入Al-10%Mg中间合金细化剂，当加入量为1.2%、保温时间90 min时，细化效果较好，Al-5%Fe合金中初生A13Fe相由未添加细化剂时的粗大板条状变为花朵状和颗粒状，并且尺寸明显减小, 从而显著提高材料的强度和塑性。关键词 Al-10%Mg中间合金；变质细化处理；过共晶铝铁合金近年来有色金属一直以质轻、延展性好等特点广泛应用于各个工业领域。尤其是铝合金的应用最为引人注目。铝具有质轻，耐蚀性良好，比强度高，有一定的延展性，外表美观，加工成型性好，可焊接等优点。加入其他合金元素制成铝合金后，不仅能够保留纯铝的优点，而且各种性能还在很大程度上得到提高。对于铝合金家族中的铝铁合金，由铁和铝形成的金属间化合物A13Fe具有许多优良的性能，如富铁相具有其独特的耐热、耐磨和抗硫化腐蚀优点，并且Al-Fe合金保持了铝合金密度小的特点，这些特点使得Al-Fe合金能适应航天器件对材料性能的要求。此外，Al和Fe是地壳中储量最为丰富的两种金属元素，也是工业中最常用的原料，来源广，价格便宜，若能用铝铁合金代替目前在工业中所应用的铁合金，将会大大降低生产成本。由于Al-Fe合金有着十分诱人的发展前景，故受到了国内外的高度重视从20世纪70年代开始，人们就把Al-Fe合金作为单独的一个合金系进行研究，将其作为一种工程结构材料应用于工业生产实际中。Al-Fe合金虽然具有许多优点，但铁在铝中的固溶度很低，一旦超过固溶度极限，便在铸造铝合金中与铝及其它元素化合，形成质脆的针状或板片状铁相，一方面，割裂基体，使用过程中会在针状富铁相尖端前沿造成应力集中，大大降低铝合金的强度，严重降低合金的力学性能；另一方面，粗大的针状相在凝固早期形成，阻碍了液体金属在补缩通道的流动，造成铸造缺陷。以上两个原因很大程度上限制了该类合金的发展。改善过共晶Al-Fe合金中富铁相的大小、形态及分布，可以充分提高Fe在Al中的优良作用。要发展Al-Fe合金，使Al-Fe合金成为一种具有实用价值的结构材料，必须找到控制和细化铁相的有效方法，尽可能地减轻或消除铁相对铝基体的不良影响。因此，控制和改善富铁相的形态，提高合金的力学性能是发展A1-Fe合金的关键。研究表明：微量镁可使铝中富铁杂质相由粗大针状或针片状变为细小的团球状或短棒状,且分布较均匀。本文研究了镁对过共晶Al-5%Fe合金组织形态的影响。由于镁元素化学性质较活泼易氧化,烧损严重,故一般均以中间合金的形式加入，铝镁中间合金中以Al-10%Mg中间合金使用的最多。 1试验1.1 试验材料试验用Al-Fe二元合金Al-5%Fe(质量分数，%，下同)由Al-10%Fe或Al-15%Fe中间合金，按铸锭成形后Fe的质量分数为5%加入相应的工业纯铝配置而成；试验用Mg为保证成分均匀以及减少烧损率，以Al-10Mg中间合金形式加入。1.2 试验方法1.2.1 熔炼过程根据二元Al-Fe合金平衡相图（图1） ，经计算配料后，将铝锭和Al-15%Fe中间合金同时加入石墨坩埚中，升温至900 ，上面撒上一层干燥的覆盖剂。当铝锭和Al-15%Fe中间合金全部熔化后，把Al-10%Mg中间合金料放置在石墨制的有孔的钟罩中，然后一起放入合金液内，钟罩放置在坩埚中部，待前一块Al-10%Mg中间合金料熔化后，保温，再加入第二块，直到所有Al-10%Mg中间合金料全部熔化。将合金液升温至950 ，静置保温2025 min，每8 min搅拌一次，最后一次搅拌后进行初次扒渣。用炉料总重量的0.3%0.5%除气剂、除渣剂精炼合金液，除气、除渣。58 min后再进行二次扒渣，之后将合金液浇入金属锭模中，获得尺寸为 30 mm100 mm的试棒。 1.2.2 金相制备过程浇铸后的铸锭冷却后取模，除去表面的飞边毛刺后从中间锯开。试样需打磨倒角处理，经金相砂纸粗磨、细磨后，再在型号为P-2型、抛盘直径为200 mm金相试样抛光机上进行粗抛和精抛。抛光后的试样用浓度为0.5%的HF水溶液腐蚀后，在光显微镜下观察分析试样的金相组织,检验细化效果。2 试验结果与分析试验重点研究了Al-10%Mg中间合金不同添加量对过共晶Al-5%Fe合金的组织形态变化规律的影响，以及Al-10%Mg中间合金细化的长效性。图2是Al-10%Mg中间合金加入量对Al-5%Fe合金中初生A13Fe相的影响。未加入Al-10%Mg中间合金时，合金中的初生A13Fe相的形貌大多为典型的粗大针状和针片状，少量为不规则的花朵状，如图2a所示；加入量为0.2%时，初生A13Fe发生了一些变化，主干还是较为发达的针状，细化效果不明显，但针状的末端已变尖变细，出现了分枝，在粗大的针状相之间，存在许多相对较小的分枝富铁相，如图2b所示；加入量达到0.6%时，初生A13Fe相的形貌发生了显著改变，生长尖端的分枝增多，以花朵状、短棒状为主，尺寸相对较小，分布也比较均匀，如图c所示；进一步增加Mg的含量，当加入量达到0.8%时，分枝现象加剧，在一次分枝上还出现了二次分枝，呈现典型的树状，组织中出现花朵状初生A13Fe相，如图2d所示；当加入量为1.2%时，初生A13Fe相的形状发生了明显不同于前三者的变化，富铁相的分枝消失，长成了较为短小的针状或者是不规则的块状，极个别长成板片状，如图2e所示；加入量为1.5%时，初生A13Fe相的尺寸明显增大，以针片状和不规则的花朵状为主，这主要是由于Mg的富集，抑制了A13Fe沿择优取向长大，使A13Fe相的尺寸增大，如图2f所示。图3 为在Al-5%Fe合金中加入1.2%的Al-10%Mg中间合金细化剂，不同保温时间合金中的初生A13Fe相的形态分布。当保温45 min时，初生A13Fe相主要以长针状形式存在于基体上，同时含有尺寸较大的不规则花朵状组织，如图3a所示；当保温时间为60 min时，相比较来看，经过60 min的保温，通过原子的溶解扩散，针状和针片状组织变得细小，初生A13Fe相主要为花朵状，但尺寸、形态不一，分布也不均匀，如图3b所示；延长保温时间至90 min时，初生A13Fe相为粗大的不规则花朵状形貌和颗粒状，如图3中c所示。时间进一步延长，组织变化更加显著，针状几乎全部转变为规则的块状和粒状。导致这种变化的原因可能是针状尖角处表面能比较大，容易扩散和溶解。 试验结果表明，随着时间的进一步延长，出现的A13Fe偏聚、沉淀、烧损等现象会明显降低其细化效果。然而，当保温时间达120 min时，仍有一定的细化效果，也就是说，Al-10%Mg中间合金细化有效时间较长，能适应大量连续生产需要，尤其对低压铸造、压力釜铸造和差压铸造等新工艺相适应，是一种良好的长效细化剂。3 结论（1）铝与过渡金属元素铁形成的A13Fe金属间化合物具有极佳的耐热、耐磨和抗腐蚀性能，并且Al-Fe合金依旧保持了Al合金密度小的特点，这些特点使得Al-Fe合金能适应航天器件对材料性能的要求。（2）微量镁可使铝中富铁杂质相由粗大针状或针片状变为细小的团球状或短棒状,且分布较均匀,从而明显提高材料的强度和塑性。（3）在过共晶Al-5%Fe合金中加入Al-10%Mg中间合金细化剂，当加入量为1.2%、保温时间为90min时，细化效果仍较好。参考文献1 王正军.Al-10Ce中间合金制备及对-Al的变质效果J.有色金属，2008，（3）：44-47.2 王正军.Al-10Ce中间合金对ZL102共晶Al-Si合金的变质研究J.中国有色冶金，2009，（2）：59-62.3 王正军.Al-10Ce中间合金制备及对-Al的变质长效性和重熔性的影响J.轻合金加工技术，2008，36（5）：18-22.4 向青春，王静媛，周振平等.铝铁合金的研究进展与应用状况J.铸造，2006，55（9）：875-879.5 陈 锋，何德坪，舒光冀.超声作用下Al-Fe合金化机制及Al-Fe合金的制备J.东大学学报，1993，23(5)：58-62.6 赵玉华，张 利，黄震威，等.钇对过共晶铝铁合金组织形貌的影响J.铸造技术，2006，27(11)：1214-1216.7 谭敦强，黎文献，唐谊平.AlFe系合金中的相及相转变J.材料导报，2003，17(5)：18-20.8 周振平，李荣德，马建超等.Mg对初生A13Fe形貌及其生长过程的影响J.热加工工艺，2004，(5)：15-17.9 蒙尔多福，王祝堂，张振录等.铝合金的组织和性能M.北京:冶金工业出版社，1988. Effect of magnesium hypereutectic aluminum alloy microstructureWang Zhengjun Liu Lianxiang Abstract:For ordinary smelting conditions a eutectic Al-Fe alloy primary iron rich in serious lacerate substrate, the performance deterioration alloy, and the element Mg-the eutectic Al-5% Fe alloys metamorphic refining processing, Mg to Al-10% Mg alloy form among to join. With optical microscope, analyzes the Al-10% Mg alloy among the grains will be refined addition amount and melt agent heat preservation time-the eutectic Al-5% Fe alloy microstructure morphology and properties of the influence. Experiment shows that: in the eutectic Al-5% Fe alloy with Al-10% Mg alloy refining among agents, when join content is 1.2%, holding time 90 min, refined effect is good, Al-5% Fe alloy A13Fe by not in the nascent add refining medium with bulky board strips into flower shapes and granular, and size significantly decrease, and improve the strength of the material and the plastic.Key words:Al-10% Mg alloy among; Metamorphic refining processing; A eutectic aluminum alloys In recent years, non-ferrous metal has been to the light, ductility is good wait for a characteristic is widely used in various industrial fields. Especially the application of aluminum alloy most noticeable. Aluminum is qualitative light, good corrosion resistance, high strength than, have certain ductility, appearance, processing molding the gender is good, can welding etc. To join other alloy element is made after the aluminum alloy, can not only keep the advantages of pure aluminum, and various performance was largely improved. For aluminum alloy aluminum alloys in the family, the iron and aluminum metal compounds formed between A13Fe is of many excellent properties, such as rich iron phase has its unique heat resistance, corrosion resistance and wear resistance of sulfide advantages, and Al-Fe alloy keep the characteristics of small aluminium alloy density, these characteristics make Al-Fe alloy can adapt to the space on the material properties of the device requirements. In addition, Al and Fe in the crust is the most abundant reserves of two kinds of metal elements, also is the most commonly used in industrial raw materials, and the source wide, cheap price, if can use aluminum alloys of the present in the industrial application of the alloys, and will greatly reduce the production cost. Because Al-Fe alloy has a very attractive prospect, it was great attention from both at home and abroad The 1970 s, people put Al-Fe alloy as separate a alloy is the study, as a kind of engineering structure materials used in industrial production practice. Al-Fe alloy although has a number of advantages, but iron in the solid solution for aluminum is very low, once more than solid solubility limit, then in casting alloy and aluminum and other elements combined, form the needle very brittle or board flake iron phase, on the one hand, separate the matrix, use process will be in the needle iron rich phase tips front cause stress concentration, and greatly reduce the strength of the aluminum alloy, severely reduces the mechanical properties of the alloy; On the other hand, the needle phase in solidification bulky early form, obstruct the liquid metal in the flow of the channel for shrink, cause the flaw in casting. Above two reasons largely limits the development of this kind of alloy. Improve a eutectic Al-Fe alloy zhongfu iron size, shape and phase of the distribution, can fully improve the Fe in Al good effect. To develop Al-Fe alloy, make Al-Fe alloy become a practical value of the structure material, must find the control and refining the effective methods in iron, as far as possible to reduce or eliminate iron relative aluminum matrix effects. Therefore, control and improve the iron rich in form, improve the mechanical properties of the alloy is the development of key A1-Fe alloy. Research shows that: trace magnesium can make the aluminum zhongfu iron impurity phase by bulky needle or needle flake into tiny football-shaped bunches or short clavite, and are uniformly distributed. This paper studies the magnesium it right Eutectic Al-5% Fe alloy organization form of influence. Because magnesium chemical properties is lively and easy oxidation, serious damage, the average all to the form of middle alloy to join, aluminum and magnesium alloy in among Al-10% Mg alloy used most of the middle. 1 test 1.1 test materials Experiment with Al-Fe two yuan alloy Al-5% Fe (mass fraction, %, similarly hereinafter) by Al-10% Fe or Al-15% Fe middle alloy, according to the quality of the bubble after forming Fe scores for 5% of the industry to join the corresponding pure aluminum configuration and become; Experiment with Mg to ensure components uniform and reduce the loss rate, to Al-10% Mg alloy form among to join. 1.2 the test method 1.2.1 smelting process According to the dual Al-Fe alloy equilibrium phase diagram (figure 1), and through calculation, ingredients, will be aluminum and Al-15% Fe alloy and join among the graphite crucibles, heating up to 900 , above and a layer of dry covering agent. When aluminum and Al-15% Fe alloy melt among all after Al-10% Mg alloy material placed in the middle of a hole of graphite the bell jar, then go into the liquid alloy, bell jar placed in central crucible, wait for a former Al-10% Mg alloy material among after molten, heat preservation, add the second piece, until all the Al-10% Mg alloy material among all melting. Will 950 temperature to liquid alloy, quiet place insulation 20 25 min, every 8 min stirring once, the last time after mixing initial grilled slag. With the total weight of the burden of 0.3% 0.5% in addition to gas agent and dregs agent refining liquid alloy, except the gas and dregs. 5 8 min again after the second pick slag, then poured into the metal liquid alloy ingot mould, get size of 30 mm x 100 mm good try. 1.2.2 Metallographic preparation process Casting the bubble cooling after take mode, removed from the surface after the flash burr sawed in the middle. Sample to burnish chamfering processing, the metallographic sand paper coarse grinding, fine grinding, and then in the model for P-type 2, PaoPan diameter for 200 mm metallographic sample polisher rough throwing and fine cast. The sample after polishing with concentration of aqueous solution for 0.5% HF corrosion, in the light microscope samples analysis of metallographic organization, inspection refined effect. 2 test results and analysis Test on Al-10% Mg alloy among different additives-the eutectic Al-5% Fe alloy form of organization change rule, and the influence of the Al-10% Mg alloy of long-term sex among refined. Figure 2 is Al-10% Mg alloy among addition amount of Al-5% Fe alloy in the influence of A13Fe born in. Not to join Al-10% Mg alloy among, the alloy A13Fe born in the shape of mostly for the typical bulky needle and needle flake, a small amount for irregular flower shapes, as shown in figure 2 a shows; Add content is 0.2%, the primary A13Fe has undergone some changes, the backbone or more developed needle, refining the effect is not obvious, but at the end of the needle has become thinner pointed, appeared branches, and in the needle is bulky, between many relatively small branch iron rich phase, as shown in figure 2 b shows; Addition amount to 0.6%, A13Fe born in the shape of a significant change happened, growth of more sophisticated branch, with flower shapes, short clavite give priority to, a relatively small size, distribution is even, as shown in figure c shows; To further increase the content of Mg, when addition amount to 0.8%, by branch phenomenon, in the first branch still appeared on secondary branch, present the typical tree, appear in the organization of A13Fe born in flowers, as shown in figure 2 d shows; When join content is 1.2%, born in the shape of A13Fe changed obviously different from the former three changes, iron rich phase to the branch of disappear, grew up and became a small needle or irregular massive, the extremely individual grown board flake, as shown in figure 2 e shows; Add content is 1.5%, the size of the primary A13Fe phase increased to needle sheets and irregular flower shapes is given priority to, it is mainly because of Mg enrichment, curb A13Fe grew up along the preferred orientation, make A13Fe phase size increases, as shown in figure 2 f as shown. Figure 3 for in Al-5% Fe alloy adding 1.2% of the Al-10% Mg alloy refining among agents, different time the alloy A13Fe born heat preservation in the shape of the distribution. When the heat preservation 45 min, born in A13Fe mainly by long needle forms exist in the matrix, and also has large size of the irregular flower shapes organization, as shown in figure 3 a shows; When the time of heat for 60 min, compared to see, after 60 min insulation, through the dissolution of the atoms diffusion, needle and needle flake organization become small, born in A13Fe mainly for flower shape, but the size, shape is differ, distribution is not even, as shown in figure 3 b shows; Extend the time of heat to 90 min, born in A13Fe for bulky irregular flower shapes morphology and granular, as shown in figure 3 c below. Further extend the time, organization change even more significant, needle almost all into the rules of massive and granular. Cause the reasons for this change may be needle sharp edges place surface can more big, easy to spread and dissolve. The results showed that with the further extend the time, the existence of a A13Fe partial gathers, the precipitation, burning the phenomenon such as significantly reduced its effect will be refined. However, when temperature time of 120 min, there is still a certain refined effect, that is, Al-10% Mg alloy refining among effective over a long period of time, can adapt to the need of continuous production, especially for low pressure casting, pressure kettle casting and differential pressure casting adapt to new technology, is a good long-term refining agent. 3 conclusions（1）Aluminum and transition metal elements of the iron to form A13Fe intermetallic has good heat resistance, wear resistance and the corrosion resistance, and Al-Fe alloy still keep the Al alloy density is small, the characteristics of these characteristics make Al-Fe alloy can adapt to the space on the material properties of the device requirements. （2）Trace magnesium can make the aluminum zhongfu iron impurity phase by bulky needle or needle flake into tiny football-shaped bunches or short clavite, and are uniformly distributed