Mg-Al-C中间合金对AZ91镁合金组织和性能的影响

通过真空烧结制备出Mg-Al-C中间合金,发现该合金可以有效地细化Mg-Al系AZ91合金的晶粒,细化后的AZ91合金力学性能显著提高,粗大且易于聚集成团的Mg17Al12相得以消除;分析认为其细化机制是在镁合金熔体中形成了大量的结晶形核质点Al4C3或Al-C-O化合物.     

Ca和Sr对AZ91D合金组织的细化作用

研究了Ca ,Sr对AZ91D合金晶粒细化的影响。试验结果表明 ,往AZ91D合金中添加少量的Ca[w(Ca) <1.0 %] ,虽然可以起到细化晶粒、提高屈服强度的作用 ,但是由于Al2 Ca相在晶界的偏聚 ,使得合金的基体脆化 ,导致了合金的抗拉强度和伸长率均下降。往AZ91D合金中添加少量的Sr[w(Sr) <0 .2 %] ,晶粒尺寸基本不发生变化。往AZ91D合金中复合添加Ca ,Sr ,不仅可以减小AZ91D合金的晶粒尺寸 ,而且还可以提高Mg合金的综合力学性能。     

MgCO3对AZ91D镁合金晶粒细化效果的研究

研究了MgCO3对AZ91D镁合金的组织的影响.利用光学显微镜和扫描电子显微镜及其电子探针观察发现,MgCO3加入使得AZ91D镁合金的二次枝晶臂间距与晶粒尺寸显著减小,主要机理是MgCO3加入后反应生成了Al4C3、Al4C3颗粒可以作为Mg的结晶核心.通过在不同温度添加不同含量的MgCO3,在790℃时添加1.0%的MgCO3使AZ91D镁合金达到最佳细化效果.对于AZ91D合金而言,MgCO3是一种良好的晶粒细化剂.     

Mg—Al—C中间合金对AZ31镁合金的晶粒细化

通过特种粉末冶金法制备了一种用于Mg-Al系合金晶粒细化的Mg-Al-C中间合金,初步分析了Mg-Al-C中间合金对AZ31镁合金的细化机理. 在该中间合金中,Al(C)固溶体分布在Mg颗粒的界面上.细化试验表明,该中间合金对AZ31(Mg-3Al-1Zn)合金有良好的细化作用.当加入3%该中间合金时,AZ31的晶粒尺寸由原来的850 μm减小到260 μm.     

Si对喷射成形AZ91镁合金微观组织的影响

在保护气氛中采用喷射成形技术制各AZ91和AZ91+2.0%Si镁合金,采用OM、SEM、XRD及TEM等技术分别对合金的微观组织进行观察和分析.结果表明:与相同成分的铸造镁合金相比,喷射成形技术显著细化合金组织;喷射成形沉积态AZ91镁合金具有均匀、细小的等轴晶组织,平均晶粒尺寸约为17 μm,离异共晶β-Mg17Al12相在晶界的偏析被有效改善:对于喷射成形AZ91+2.0%Si镁合金,喷射成形过程中高的冷却速度抑制了Mg2Si相的长大,细小的Mg2Si相呈现为近球形或多边形态,与基体结合良好且弥散分布,并可以作为а-Mg异质彤核核心,使合金组织得到充分细化.     

新型Al-Ca-C中间合金对AZ91合金的细化作用

以Al粉、CaC2粉为原料,采用粉末冶金及原位合成法制备了一种新型Al-Ca-C中间合金用于AZ91合金的晶粒细化,Al-Ca-C中间合金中含有Al4C3、CaAl2、CaAl4相.试验表明,该中间合金对AZ91镁合金有良好的晶粒细化作用.当加入1.0％的Al-Ca-C中间合金时,AZ91合金的晶粒尺寸由原来的120～150 μm减小到40～50 μm.分析认为镁合金的细化机理为,Al4C3充当了α-Mg的异质形核核心,熔体中Ca与C原子则由于成分过冷进一步促进了晶粒细化.     

Al-C和Al-Ti-C中间合金对AZ91合金晶粒的细化

制备出两种用于AZ91合金晶粒细化的Al-C和Al-Ti-C中间合金.结果表明:这两种中间合金对AZ91合金均有良好的晶粒细化作用.向AZ91合金中加入1%的Al-C中间合金可使晶粒由原来的约130μm减小至65μm左右;向AZ91合金中加入1%的Al-TI-C中间合金可使晶粒由原来的约130μm减小至45μm左右.然而,两种中间合金添加量分别大于1%时,晶粒尺寸没有进一步的变化.分析认为:Al-C和Al-Ti-C中间合金起晶粒细化作用的分别是Al4C3相和Al4C3和TiC复合相.     

Al-Ti-C对AZ91D合金显微组织影响

研究了不同Al-Ti-C含量对AZ91D镁合金铸态及T6态金相组织的影响。分析表明,在一定的范围内,随着Al-Ti-C中间合金的加入,AZ91D合金晶粒尺寸逐渐变小,晶粒被细化;影响AZ91D合金晶粒尺寸的原因是Al-Ti-C中间合金中存在Al4C3和TiC复合颗粒形核相。     

微量Si、Ba、Sn对AZ91铸态组织的影响

研究了Si、Ba、Sn元素对AZ91镁合金铸态组织的影响。结果表明,添加少量的Si能够细化AZ91合金晶粒,但当Si含量(质量分数,下同)达0.50%时,会产生粗大的汉字状Mg2Si相。向AZ91-0.5Si合金中加入微量的Ba后,粗大的Mg2Si相消失,这与合金中形成了Al4Ba相有关。添加一定量的Sn能够形成高熔点的Mg2Sn相,对合金有细化晶粒的作用,添加量为0.50%时β(Mg17Al12)相由网状变为弥散的颗粒状。分析认为,0.50%的Sn可以提高Al原子在α(Mg)中的固溶度。     

熔体处理及电磁搅拌对AZ91D合金组织的影响

利用金相显微分析等手段，研究了熔体处理及电磁搅拌对AZ91D合金组织的影响。结果表明，C粉对AZ91D合金晶粒具有明显的细化作用，优于C2Cl6和Al—10Sr间合金，无水FeCl3、Al-5Ti—B测效果甚微。熔体处理与电磁搅拌复合作用使AZ91D合金晶粒转化为均匀细小的类球状半固态组织，作用优于单纯的电磁搅拌。     

Preparation of submicrocrystal Al-Ti-B master alloy and its influence on microstructure and properties of AZ91D

To improve the mechanical properties of AZ91D magnesium alloy,the submicrocrystal Al-Ti-B master alloy was prepared with copper mold inject casting method,and the influence of submicrocrystal Al-Ti-B master alloy on the microstructure and mechanical properties of AZ91D was investigated.Results show that,the distribution of Ti B_2 phase in submicrocrystal Al-Ti-B alloy is even and disperse,and the average size of Ti Al_3 phase is reduced from 10-30μm to～1μm.The properties of AZ91D refined with submicrocrystal Al-Ti-B master alloy are better than that with coarse-grained Al-Ti-B master alloy without copper mold inject casting.The tensile strength,elongation and Brinell hardness of AZ91D are increased by 10.6%,25%and 18.1%,respectively.Therefore,refinement of AZ91D with submicrocrystal Al-Ti-B that is obtained by copper mold inject casting is an effective method to improve its mechanical properties.     

Effect of cerium addition on microstructure and corrosion resistance of die cast AZ91 magnesium alloy

A novel AZ91 Ce containing magnesium alloy characterized by excellent corrosion resistance is fabricated by adding rare earth Ce (cerium) in the form of a Mg‐Ce master alloy. The metallographic investigation shows that Ce added to AZ91 can obviously decrease the size of β‐Mg₁₇Al₁₂ and forms Al₁₁Ce₃ intermetallic compounds in the shape of fine needles. The corrosion tests and electrochemical measurements indicate that the corrosion resistance of AZ91 Ce containing magnesium alloy is obviously higher than that of AZ91. Furthermore, increasing the content of Ce in the magnesium alloy can further enhance the corrosion resistance. X‐ray photoelectron spectroscopy (XPS) reveals that Ce can be incorporated into corrosion products in the form of CeO₂ in the course of corrosion. Based on the preliminary analysis, the addition of Ce can improve the corrosion resistance of AZ91 by decreasing the size of β‐Mg₁₇Al₁₂ and enhancing the protective effectiveness of corrosion products.     

Non-flux purification behavior of AZ91 magnesium alloy

The effects of non-flux purification techniques on the mechanical properties and microstructure of AZ91 magnesium alloy were investigated by ICP,OM,XRD and SEM.The results show that Ar spraying with high flow rate could remove non-metallic inclusions and improve the mechanical properties of AZ91.The alloy obtains the best properties after argon spraying for 30 min at the melt temperature of 740 °C.The ceramic foam filter(CFF) could effectively improve the ultimate tensile strength and elongation of AZ91 alloy,especially the elongation,which increase with increasing pores per inch(ppi) and the thickness of CFF.Non-flux purification does not change the microstructure of AZ91 alloy.However,filtration has a certain effect on the fracture pattern of AZ91 alloy.To improve the mechanical properties effectively,both filtration and gas spraying should be utilized together.     

Mechanical properties and microstructures of a wrought AZ91 alloy

Effects of hot plastic deformation on microstructures and tensile properties of AZ91 alloy were investigated. Compared with as-T4 microstructures, the as-extruded samples of AZ91 alloy with fine grains exhibit better strength and ductility due to dynamic recrystallization. The succeeded rotation forging also provides freer grains while the strength increases, but the elongation decreases. Simultaneously, wrought AZ91 alloy shows more balance properties than as-T4 condition ones. An interesting elongation of 228.5% is attained in the as-extruded AZ91 alloy in spite of the coarse grains with the size of 85 μm. The two-step method enhances the superplastic property of AZ91 alloy. The microstructure is still keeping the same scale of grains after superplastic testing.     

Machining characteristics of fine grained AZ91 Mg alloy processed by friction stir processing

AZ91 Mg alloy was considered and friction stir processing (FSP) was adopted to achieve grain refinement to investigate the effect of grain size and secondary phase on machining characteristics during drilling at various speeds and feeds. Super saturated AZ91 Mg alloy was obtained after FSP and the grain refinement was achieved from (166.5±8.7) µm to (21.7±13.5) µm. Surprisingly, hardness reduced for FSP AZ91 Mg alloy (88.95±6.1) compared with AZ91 alloy (108.2±15.6), which was attributed to the reduced secondary phase. However, the mean cutting force for FSP-treated (FSPed) AZ91 Mg alloy was marginally increased. The edge damage of the drilled holes was lower for FSPed AZ91 Mg alloy compared with unprocessed AZ91 Mg alloy. Hence, it can be understood that the grain refinement may slightly increase the cutting forces during drilling but better edge finishing can be achieved in machining of AZ91 Mg alloy.     

Application of cyclic upsetting-extrusion to semi-solid processing of AZ91D magnesium alloy

The microstructural evolution of AZ91D magnesium alloy prepared by means of the cyclic upsetting-extrusion and partial remelting was investigated. The effects of remelting temperature and holding time on microstructure of semi-solid AZ91D magnesium alloy were studied. Furthermore, tensile properties of thixoextruded AZ91D magnesium alloy components were determined. The results show that the cyclic upsetting-extrusion followed by partial remelting is effective in producing semi-solid AZ91D magnesium alloy for thixoforming. During the partial remelting, with the increase of remelting temperature and holding time, the solid grain size increases and the degree of spheroidization tends to be improved. The tensile mechanical properties of thixoextruded AZ91D magnesium alloy components produced by cyclic upsetting-extrusion and partial remelting are better than those of the same alloy produced by casting.     

Al-5C中间合金对AZ31镁合金的细化机理

采用粉末原位合成工艺制备Al-5C中间合金,研究Al-5C中间合金对AZ31镁合金晶粒细化的影响及细化机理。结果表明：Al-5C中间合金由α（Al）和 Al 4 C 3两相组成,Al 4 C 3颗粒的尺寸分布由烧结时间控制。Al-5C中间合金能显著地细化AZ31镁合金晶粒尺寸,当Al-5C中间合金添加量低于2%时,随着Al-5C中间合金添加量的增加,AZ31镁合金晶粒尺寸减小。晶粒细化机理是由于 Al4C3与 Mn 反应生成的Al-C-Mn 颗粒能作为初生α-Mg晶粒的异质形核基底,从而细化晶粒。     

Effect of intermetallics on susceptibility of Mg alloy welds to liquation cracking

ABSTRACT

The circular-patch welding test was used to study the liquation and liquation cracking of AZ-series Mg alloys. A heat treatment was carried out on the as-received AZ91 alloy to dissolve the γ(Mg₁₇Al₁₂) particles before welding. The circular-patch welding test was then conducted on the heat-treated, as-received AZ91 alloy using AZ61 and AZ91 filler wires. The results showed that the susceptibility of AZ91 alloy to liquation and liquation cracking was significantly reduced by the dissolution of massive γ(Mg₁₇Al₁₂) particles via a heat treatment before welding as the liquation mechanism was changed. Both constitutional liquation and incipient melting occurred in the partially melted zone of the as-received AZ91 welds, while only incipient melting occurred in the heat-treated AZ91 welds.     

Effect of Ca and Y additions on oxidation behavior of AZ91 alloy at elevated temperatures

In order to develop the ignition-proof magnesium alloy, the effect of alloying elements, Ca and Y, on the oxidation behavior of AZ91 magnesium alloy at elevated temperatures was investigated. The ignition-proof performance, oxide products and oxidation kinetics of Ca- and Y-containing AZ91 alloys were studied. The results indicate that the proper addition of Ca can increase the ignition point of AZ91 alloy greatly. However, the oxide film of Ca-bearing AZ91 alloy formed at elevated temperature is thick and brittle, which is prone to crack in melting and cooling process. In addition, the oxide film of AZ91-xCa alloy is incompact and cannot inhibit the diffusion of reaction particles. The oxide film of AZ91-xCa alloy turns to thin and plastic one after Y is added, and the density of the oxide film increases greatly due to the formation of composite oxide film composed of MgO, CaO and Y2O3.     

汽车发动机用AZ91D合金的表面喷涂与性能

采用热喷涂工艺在压铸态AZ91D合金表面制备了Al涂层,研究了热处理温度和保温时间对AZ91/Al涂层界面组织形貌的影响,并对比分析了扩散层的耐腐蚀性能和耐磨性能。结果表明,热处理前Al涂层与基材为机械结合,热处理后Al涂层与AZ91合金基材的界面处可形成冶金结合扩散层,且随着保温时间延长,扩散层厚度不断增加;热处理温度在375 ℃以下时扩散层主要由β-Mg₁₇Al₁₂相构成,375 ℃×8 h热处理后为α-Mg+β-Mg₁₇Al₁₂相,425 ℃×1 h热处理后为γ-Mg₂Al₃和β-Mg₁₇Al₁₂相。AZ91合金基材和扩散层腐蚀电位从高至低顺序为γ>β>α+β>AZ91合金基材,扩散层的腐蚀电流密度均低于AZ91合金基材,阻抗谱图中容抗弧半径从大至小顺序为γ>β>α+β>AZ91合金基材,扩散层的耐腐蚀性能均优于AZ91合金基材;γ、β和α+β扩散层的摩擦稳定性系数都高于AZ91合金基材,而磨损速率和磨痕宽度都要小于AZ91合金基材,其中β扩散层的磨损速率和磨痕宽度最小,具有最佳的抵抗磨损的能力。