挤压铸造与超声处理对铸造铝锂合金组织与性能的影响

目的 研究挤压铸造与超声处理工艺对铸造铝锂合金组织与性能的影响规律,分析工艺改变对组织细化及性能提升的作用机理,解决传统重力铸造下铝锂合金性能较差的问题。方法 将挤压铸造（SC）与超声处理（UT）相结合制备Al-2Li-2Cu-0.5Mg-0.2Zr合金,在熔体超声2 min后,以50 MPa的挤压力制备合金,探究各工艺对铸造铝锂合金显微组织与力学性能的影响。结果 与传统的重力铸造（GC）相比,SC合金的孔隙率和成分偏析显著降低,晶粒尺寸也明显减小,特别是经过UT+SC处理的合金得到了进一步优化。经UT+SC处理后,Al-2Li-2Cu合金的极限抗拉强度（UTS）、屈服强度（YS）和伸长率分别为235 MPa、135 MPa和15%,与GC合金相比,分别提高了113.6%、28.6%、1 150%,与SC合金相比,分别提高了5.4%、3.8%、15.4%。结论 UT+SC工艺能明显提升铸造铝锂合金的性能。UT+SC制备的Al-Li合金的强度和伸长率的提高归因于孔隙率的降低、晶粒细化和第二相的均匀分布。将挤压铸造与超声处理相结合制备铸造铝锂合金解决了重力铸造下合金性能较差的问题,为满足航...     

微量Sr和Mn对Mg-8Li-3Al变形合金力学性能的影响

用光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)和电子万能试验机对比研究了微量添加Sr和Mn对Mg-8Li-3Al合金组织和力学性能的影响,结果表明:基础合金Mg-8Li-3Al主要由α-Mg,β-Li和Al12Mg17金属间化合物组成,Sr和Mn的加入使合金中形成了Al4Sr和Al2Mn3等金属间化合物。合金元素Sr和Mn对合金组织均有细化效果,Sr的细化效果优于Mn。添加Sr和Mn后合金的强度均有所提高,其中挤压态Mg-8Li-3Al-0.5Sr-0.5Mn合金的σb=242.15 MPa,σ0.2=206.96 MPa,δ=22.43%,比Mg-8Li-3Al镁合金的力学性能分别提高了14.98%,28.11%和8.31%。     

Mg-9Gd-4Y-2Zn-0.5Zr镁合金的微观组织与性能研究

目的 研究挤压比对热挤压制备的Mg-9Gd-4Y-2Zn-0.5Zr(VW94)镁合金微观组织、拉伸性能和抗腐蚀性的影响,并揭示挤压比对组织和性能演变的影响机制。方法 用挤压比为16和35的热挤压工艺制备了Mg-9Gd-4Y-2Zn-0.5Zr(VW94)镁合金,通过光镜（OM）、X射线衍射仪（XRD）、扫描电子显微镜（SEM）等手段表征并分析了不同挤压比下的微观组织,进一步通过拉伸测试和电化学测试评估合金的力学性能和腐蚀速率,并通过SEM表征断口形貌和腐蚀形貌,分析其断裂方式和腐蚀机制。结果 挤压比的大小并不会影响镁合金的相成分,镁合金主要由α-Mg基体及晶界处的LPSO相组成。当挤压比为16时,第二相数量更多,平均晶粒尺寸更小;当挤压比增大到35时,合金的再结晶程度更高,其晶粒尺寸分布更加均匀。性能表征结果发现,挤压比为16的VW94合金的力学性能更优,其抗拉强度及伸长率分别达到376.3MPa和13.3%,但是挤压比为35的VW94合金的耐腐蚀性能更好。结论 挤压比虽然不会影响相的种类,但是会影响第二相的含量和晶粒尺寸,从而进一步影响拉伸性能和腐蚀速率,因此可以通过优化挤压比协同...     

不同路径等通道转角挤压双相Mg-10.73Li-4.49Al-0.52Y合金的组织与力学性能

采用等通道转角挤压（ECAP）工艺在573 K温度下以Bc、A和C三种工艺路径对双相Mg-10.73Li-4.49Al-0.52Y镁锂合金分别进行1-4道次挤压变形,利用光学显微镜、扫描电镜和X射线衍射等研究变形后合金组织。结果表明,三种路径ECAP变形后,α相和β相晶粒均得到显著拉长和细化;4道次变形后,路径A获得片...     

高Ca/Al比的Mg-Al-Ca合金的超塑性

针对3种高Ca/Al比的Mg-Al-Ca合金(Mg-3.7Al-3.8Ca,Mg-4.4Al-4.5Ca和Mg-4.9Al-5.0Ca)的超塑性行为展开研究,研究结果表明,铸态镁合金具有二次相Al2Ca分布于晶界的枝晶结构。经挤压后,合金的晶粒被细化,二次相也被细化为更小的粒子。这些合金在400℃时表现出很高的伸长率,Mg-4.9Al-5.0Ca在400℃时3.6×10-4 s-1应变速率下获得最大伸长率572%。超塑性流变的变形机制为晶格扩散(DL)控制的晶界滑移(GBS)。对于挤压态Mg-4.9Al-5.0Ca合金,大部分高温稳定相Al2Ca粒子尺寸为80nm,对晶粒长大的抑制作用强烈,在晶界滑移时协调变形,因此在3种合金中Mg-4.9Al-5.0Ca具有最好的超塑性。     

Si对AM30变形镁合金组织和力学性能的影响

为了提高Mg-3Al-0.4Mn合金的常温力学性能,研究了铸态和挤压态下Si含量对AM30合金的组织和力学性能的影响.结果表明,增加Si的添加量会生成粗大的汉字状的Mg2Si相,不利于提高合金的力学性能;但经过挤压后,呈汉字状Mg2Si相破碎,变成颗粒细小的Mg2Si相,晶粒细化,有利于提高合金的性能.     

固溶体Mg-5Al-xGd合金的制备及其压缩性能EI北大核心

利用Gd(0.00%,0.25%,0.50%,0.75%,1.00%,质量分数,下同)元素和凝固压力(3 GPa)调控Mg-5Al合金凝固组织结构,对合金样品进行压缩测试,并研究组织结构与室温压缩性能相关性。结果表明:常压石墨型铸造下,仅Mg-5Al-0.75Gd合金获得了晶界无共晶相生成、粒状Al2Gd相弥散分布在基体上、晶粒平均尺寸约为85μm的固溶体组织,其抗压强度和最大压缩应变分别为379 MPa和33.46%,高于存在晶间第二相的合金。3 GPa高压下,Gd含量≤0.25%合金的凝固组织为单一固溶体,Gd含量≥0.50%合金的晶界(枝晶间)有共晶Al_(2)Gd相生成。固溶体Mg-5Al-0.25Gd合金的平均晶粒尺寸是74μm,抗压强度是402 MPa,最大压缩应变是33.61%。Mg-5Al-0.75Gd合金的平均晶粒尺寸是38μm,抗压强度和最大压缩应变分别是341 MPa和25.12%,其性能低于Mg-5Al-0.25Gd合金。可见,晶间Al,Gd元素的存在形式是影响铸造Mg-Al合金力学性能的重要因素。     

Sb对Mg-5Al-2Sr合金组织和性能的影响

采用表面活性元素Sb微合金化的方法制备了Mg-5Al-2Sr-xSb(x=0,0.3,0.6,1.0)合金,通过金相显微镜、X射线衍射仪、扫描电镜和力学性能测试等方法研究了Sb含量对Mg-5Al-2Sr合金微观组织和力学性能的影响.结果表明,Mg-5Al-2Sr-xSb合金铸态组织主要由枝晶α-Mg、沿晶界或分布在枝晶间的层状或离异共晶的Al4Sr相、块状三元Mg9Al3Sr相(τ相)和颗粒状SbSr2相组成,随着Sb含量的增加,Sb-Sr2相的数量逐渐增多,τ相逐渐减少.Sb的质量分数为0.6%时,断续分布的Al4Sr相和细小弥散分布的Sb-Sr2相能够提高Mg-5Al-2Sr合金的室温和高温(150℃)机械性能.     

添加稀土Gd对Mg-6Al镁合金组织和耐蚀性的影响

Mg-6Al镁合金具有较好的铸造性能和力学性能,目前鲜见单一稀土元素对其腐蚀性能影响的报道。通过合金制备、微观组织分析和耐蚀性测试等方法研究了稀土Gd添加量对Mg-6Al镁合金微观组织和耐蚀性能的影响。OM、SEM、EDS、XRD分析结果表明,稀土Gd的添加改善并细化了Mg-6Al合金的铸态组织,形成杆状或块状的Al2Gd新相;动电位极化、浸泡试验等测试结果表明Gd的添加显著提高了Mg-6Al合金在3.5%NaCl溶液中的耐腐蚀性能,Mg-6Al-2%Gd镁合金的腐蚀速度最小,为0.83 mm/a,且腐蚀后组织较为致密,腐蚀产物和腐蚀坑均变小,Mg-6Al-x Gd合金的腐蚀产物主要为Mg(OH)2。     

均质化制度对Mg-Li合金显微组织和机械性能的影响

研究了超轻镁锂变形合金热处理后的合金显微组织和机械性能。镁锂合金在室温条件下具有非常良好的延展性，Mg—Li—Zn系变形镁合金铸锭经不同温度、时间均匀化退火后的组织、硬度以及冷轧性能进行了研究。结果表明。Mg．9％Li-2％Zn-2％Ca合金在573K温度均匀化退火12h后合金铸锭组织均匀；而对于Mg-9％Li-2％Zn合金，523K温度均匀化退火24h后组织较好。     

Microstructural evolution,mechanical properties and corrosion behavior of as-cast Mg-5Li-3Al-2Zn alloy with different Sn and Y addition

Influences of Sn and Y on the microstructure,mechanical properties,and corrosion behavior of as-cast Mg-5Li-3Al-2Zn (LAZ532) alloy were investigated.The addition of Sn and Y refines grains and results in the formation of Mg2Sn and Al2Y phases,thus improving the mechanical properties of alloy by second phase strengthening and grain refinement strengthening.As-cast LAZ532 alloy shows typical filiform corrosion morphology,and the addition of Sn and Y does not change the corrosion mode of alloy.Ascast LAZ532-0.8Sn-1.2Y alloy shows excellent mechanical properties with yield strength of 166.2 MPa,ultimate tensile strength of 228.6 MPa and elongation of 14.8 ％,and exhibits the best corrosion resistance with the smallest corrosion current density and the lowest anodic dissolution rate.     

Effect of Sn on the Microstructure and Mechanical Properties of Mg-5Al-2Si Alloys

The effect of Sn addition on the microstructures and mechanical properties of Mg-5Al-2Si alloys was investigated with variations of Sn contents （3 and 6 wt pct）. The microstructure of the alloy was characterized by the presence of Mg2Sn particles within matrix and at grain boundaries. As the Sn contents increased, yield and ultimate tensile strength were increased at room temperatures and 150℃. Creep properties were improved with the increasing amount of Sn due to the fine precipitation of Mg2Sn phases within grain during creep.     

Microstructure and Mechanical Properties of Mg-Al-Ca-Nd Alloys Fabricated by Gravity Casting

The aims of this study are to investigate the effects of Nd addition in the Mg-Al-Ca alloys on microstructure and mechanical properties.Microstructure of as-cast Mg-5Al-3Ca alloy containing Nd consists ofα-Mg matrix, eutectic phase and Al-Nd rich intermetallic compound.As Nd addition was increased,α-Mg matrix morphology was changed from dendritic to equiaxed grains and average value of grain size was decreased.Nd addition to Mg-5Al-3Ca based alloys resulted in the formation of Al-Nd rich intermetallic compounds at grain boundary andα-Mg matrix grains.And these Al-Nd rich intermetallic compounds were dispersed homogeneously.In these alloys,two kinds of eutectic phases were observed,i.e.coarse irregular-shape structure at grain boundary and fine needle-shape structure in theα-Mg matrix grain.It is found that the ultimate strength showed the maximum value of 271 MPa at Mg-5Al-3Ca-2Nd alloy and elongation was decreased as the addition of Nd was increased.     

热处理对双相Mg-8Li-4Al-3Zn-La合金组织与性能的影响

分别对原始态的双相Mg-8Li-4Al-3Zn-La合金进行固溶及退火处理,通过光学显微镜、扫描电镜以及X射线衍射等方法研究合金在不同热处理状态下微观组织的变化,测定了合金硬度及拉伸性能并分析了断口。研究结果表明,经固溶处理后合金抗拉强度明显提高,由原来的194MPa提升到243MPa,延伸率由18%降至9%;而退火处理后其强度没有提升,塑性反而下降。此外,合金中两相组织与第二相分布具有明显差异,使得各相性能及其对热处理的反应不同。     

Blood compatibility of zinc–calcium phosphate conversion coating on Mg–1.33Li–0.6Ca alloy

Magnesium alloys as a new class of biomaterials possess biodegradability and biocompatibility in comparison with currently used metal implants. However, their rapid corrosion rates are necessary to be manipulated by appropriate coatings. In this paper, a new attempt was used to develop a zinc-calcium phosphate (Zn-Ca-P) conversion coating on Mg-1.33Li-0.6Ca alloys to increase the biocompatibility and improve the corrosion resistance. In vitro blood biocompatibility of the alloy with and without the Zn-Ca-P coating was investigated to determine its suitability as a degradable medical biomaterial. Blood biocompatibility was assessed from the hemolysis test, the dynamic cruor time test, blood cell count and SEM observation of the platelet adhesion to membrane surface. The results showed that the Zn-Ca-P coating on Mg-1.33Li-0.6Ca alloys had good blood compatibility, which is in accordance with the requirements for medical biomaterials.     

Effects of samarium on microstructures and tensile properties of Mg-5Al-0.3Mn alloy

Microstructures and tensile properties of Mg-5Al-0.3Mn-xSm (x = 0, 1, 2 and 3 wt.%) alloys prepared by metal mould casting method were investigated. It was demonstrated that Mg-5Al-0.3Mn alloy was mainly composed of α-Mg and β-Mg₁₇Al₁₂ phases. However, the other two precipitates (Al₁₁Sm₃ and Al₂Sm) were observed along grain boundaries in the alloys containing Sm. The amount of Al₁₁Sm₃ and Al₂Sm precipitates was increased with the increment of Sm content. Meanwhile, volume fraction of β-Mg₁₇Al₁₂ phase was decreased. Moreover, the morphology of β-Mg₁₇Al₁₂ was altered from bulk bone-like shape to spherical one. Tensile results showed that Mg-5Al-0.3Mn-2Sm alloy exhibited the highest tensile properties both at room temperature and 150 °C. Compared with ultimate tensile strength (UTS), yield strength (YS) and elongation (?) of Mg-5Al-0.3Mn alloy, UTS, YS and ? of Mg-5Al-0.3Mn-2Sm alloy were enhanced by 30%, 45% and 35% at room temperature, and by 17%, 48% and 96% at 150 °C, respectively. The improvement of tensile properties was attributed to the decreased amount of β-Mg₁₇Al₁₂ and its refined morphology, and high thermal stable Al₁₁Sm₃ and Al₂Sm precipitates which effectively prohibited dislocation movement and grain boundary sliding during deformation process.     

An additively manufactured Al-14.1Mg-0.47Si-0.31Sc-0.17Zr alloy with high specific strength,good thermal stability and excellent corrosion resistance

A novel Al-14.1 Mg-0.47 Si-0.31 Sc-0.17 Zr alloy was applied in the printing process of selective laser melting(SLM),and the corresponding microstructural feature,phase identification,tensile properties and corrosion behavior of the Al Mg Si Sc Zr alloy were studied in detail.As fabricated at 160 W and 200 mm/s,the Mg content of bulk sample decreased to 11.7 wt%due to the element vaporization at high energy density,and the density of this additively manufactured Al Mg Si Sc Zr alloy was 2.538 g/cm³,which is4.2%8.5%lighter than that of other SLM-processed Al alloys.After heat-treated(HT)at 325℃and 6 h,the microstructure was almost unchanged with an alternate distribution of fine equiaxed crystals and coarse columnar crystals.Nano-sized Al3(Sc,Zr)and Mg₂Si phases precipitated dispersedly in the Al matrix,and the tensile strength increased from 487.6 MPa to 578.4 MPa for precipitation strengthening and fine grain strengthening.With a fine grain size of 2.53μm,an excellent corrosion resistance was obtained for the as-printed(AP)Al Mg Si Sc Zr alloy.While the corrosion resistance of HT sample decreased slightly for the formation of non-dense oxide layer and pitting corrosion induced by diffuse precipitation distribution.This SLM-printed Al Mg Si Sc Zr alloy with high specific strength,good thermal stability and excellent corrosion resistance has broad prospects for the aerospace and automotive applications.     

Exfoliation corrosion of extruded Mg-Li-Ca alloy

Exfoliation on as-extruded Mg-1 Li-1 Ca magnesium alloy was investigated after an immersion in 3.5 wt%NaCl aqueous solution for 90, 120 and 150 days through optical microscope, digital camera, scanning electron microscope, electrochemical workstation, scanning Kalvin probe, X-ray diffraction and Fourier transform infrared spectroscope. The results demonstrated that exfoliation corrosion occurred on extruded Mg-1 Li-1 Ca alloy due to elongated microstructure parallel to surface, and delamination of lamellar structure resulted from galvanic effect and wedge effect. Skin layer with fine grains exhibited better corrosion resistance, whereas the interior with coarse grains and the intermetallic compound,Mg_2 Ca particles existing in a fibrous structure, dispersed along grain boundaries and extrusion direction in a line. Furthermore, galvanic effect between Mg_2 Ca particles and their neighboring a-Mg matrix facilitated dissolution of Mg_2 Ca particles and a-Mg matrix; wedge effect was caused by formation of corrosion products. Exfoliation corrosion of extruded Mg-Li-Ca alloys might be a synergic effect of pitting corrosion,filiform corrosion, intergranular corrosion and stress corrosion. Finally, exfoliation corrosion mechanism was proposed.