Effect of SiC volume fraction on the age-hardening behavior in SiC particulate-reinforced 6061 aluminum alloy composites

The age-hardening behavior in the SiC particulate-reinforced 6061 aluminum alloy composites (SiCp/6061 Al alloy composites) was investigated using hardness measurement, calorimetric technique and transmission electron microscopy. The aging time for the peak hardness in 10%SiCp/6061 Al and 20%SiCp/6061 Al alloy composites was shorter than that of the unreinforced 6061 Al alloy, and the age-hardening was most accelerated in the 20%SiCp/6061 Al alloy composite. It is induced from the high density of dislocations in SiCp/6061 Al alloy composites which act as heterogeneous nucleation sites of precipitates and as a high diffusivity path of alloy elements. The precipitation sequence and the aspect of precipitates in the 6061 Al alloy cannot be affected considerably by the presence of SiC particulate and the volume fraction of SiC particulate. The activation energies for the formation of the intermediate β' phase in the unreinforced 6061 Al alloy, 10%SiCp/6061 Al and 20%SiCp/6061 Al alloy composite were 142.6 kJ/mol, 127.3 kJ/mol, 106.1 kJ/mol, respectively.     

亚微米Al2O3颗粒表面稀土改性及其对6061Al复合材料时效行为的影响

采用液相包裹法对亚微米Al2O3颗粒进行稀土表面改性，用挤压铸造法制备表面经稀土改性的Al2O3p／6061Al复合材料．对颗粒表面经稀土改性前后增强6061Al复合材料在不同温度下的时效析出行为进行分析研究．结果表明：改性后的亚微米Al2O3粉体颗粒表面Y2O3包裹均匀，其增强的复合材料在不同时效阶段的硬度值均较改性前有明显提高．且随着时效温度的升高，Mg2Si析出过程加快，时效峰提前，呈现出硬度值变小的趋势，透射电镜观察表明，表面改性颗粒增强的复合材料基体中存在一定量的位错和析出相；而改性前复合材料却呈现出位错和析出相极其稀少的组织特征．分析了改性前后复合材料时效组织形成的原因。     

热处理对挤压铸造TiB2P/6061Al复合材料组织与性能的影响

采用挤压铸造法制备了不同体积分数的TiBzv／6061Al复合材料，利用扫描电镜、透射电镜、硬度计、三点弯曲等手段对复合材料的组织与力学性能进行了研究，分析了热处理工艺对其组织性能的影响。结果表明：不同的热处理条件下TiB2P／6061Al复合材料的组织不同：退火态时观察到再结晶晶粒和少量位错：时效态时观察到大量的位错和析出相，界面产物尺寸比退火态时相对大些，且在界面附近的基体中存在明显的无析出区。热处理状态对弹性模量的影响不大，但对材料的硬度和抗弯强度影响较大。45％TiB2v／6061Al复合材料时效处理后硬度和抗弯强度分别比退火态时提高了40％和23％。     

Improvement of high-temperature strength of 6061 Al matrix composite reinforced by dual-phased nano-AlN and submicron-Al2O3 particles

Nano-AlN and submicron-Al₂O₃ particles were simultaneously utilized in a 6061 Al matrix composite to improve the high-temperature strength. According to the SEM and TEM characterization, nano-AlN and submicron- Al₂O₃ particles are uniformly distributed in the Al matrix. Brinell hardness results indicate that different from the traditional 6061 Al matrix alloy, the aging kinetics of the composite is obviously accelerated by the reinforcement particles. The T6-treated composite exhibits excellent tensile properties at both room temperature and elevated temperature. Especially at 350 °C, the T6-treated composite not only has a high yield strength of 121 MPa and ultimate tensile strength of 128 MPa, but also exhibits a large elongation of 11.6%. Different strengthening mechanisms of nano-AlN and submicron-Al₂O₃ particles were also discussed in detail.     

Effects of heat treatments on AA6061 aluminum alloy deformed by cross-channel extrusion

In this study, the relationship between microstructures and mechanical properties of the cross-channel extrusion (CCE) processed AA6061 alloy caused by different heat treatments were investigated. The ultimate tensile strength of the homogenized AA6061 can be strengthening to 194 MPa after extruded at 448 K for 8 passes. After T6 treatment, the strength was increased from 194 to 323 MPa caused by the formation of fine precipitates; however, the grains were coarsened. The Post-CCE aging treatment was applied on AA6061 alloy that the alloy was processed in supersaturated state at 448 K for 8 passes, and then artificial aged. A higher tensile strength of 364 MPa which is 13% higher when compared with the T6 treated sample was obtained since it consisted of fine-grained matrix with grain structure size of 0.2–0.5 μm and precipitation hardening effect. It demonstrates that the Post-CCE aging treatment is a suitable method for producing a heat treatable Al alloy with improved strength when applied to CCE process.     

Effect of nano-silver on microstructure,mechanical and tribological properties of cast 6061 aluminum alloy

Al6061 matrix with different amounts of nano-silver (1% and 2%) was produced by stir-casting method. Produced samples were characterized by hardness, tensile, compression and wear tests. The hardness of the specimens at room temperature was measured by Brinnell hardness testing machine. The magnitude of hardness increased evidently with the function of the mass fraction of the nano-Ag particle. The polished specimens were examined with an optical microscope. The fracture surfaces of tensile and compressive specimens were further examined by scanning electron microscopy. Wear mechanisms were discussed based on the scanning electron microscopy observations of worn surface and wear debris morphology. There is an increase in compressive strength, ultimate tensile strength, elongation and wear resistance of the Al-Ag composites compared with base alloy. The execution of stir-casting technique is relatively homogenous and fine microstructure which improves the addition of reinforcement material in the molten metal. The results show that Al6061-nano-silver which is the best combination of hardness can replace the conventional material for better performance and longer life.     

AGE STRENGTHENING OF DIFFUSION WELDED JOINT OF Al_2O_(3p)/6061Al COMPOSITE

1.IntroductionAluminummatrixcompositehascometobeusedforvariouskindsofstructUreowingtoitsexcellentpropertiessuchashighspecificstrength,highspecificmodule,highwearability,andbecomeemphasisanddirectionofresearchinnewmaterialsscience.ButthespecialcompositionsOfaluminummatrixcompositealsodetendnethecharacteristicthatitishardtobesubjecttosecondalworking,especiallytheweldingtechnologyproblemisamajorfactorhinderingitfurthertodevelOP.Thestudyondiffusionweldingtechnologyforaluminummatrixcompositeshowe…     

Effect of Thermal Cycling Treatment on Microyield Behavior of Al_2O_3p/Al Composite

ＥｆｅｃｔｏｆＴｈｅｒｍａｌＣｙｃｌｉｎｇＴｒｅａｔｍｅｎｔｏｎＭｉｃｒｏｙｉｅｌｄＢｅｈａｖｉｏｒｏｆＡｌ２Ｏ３ｐ／ＡｌＣｏｍｐｏｓｉｔｅＬｉＹｉｃｈｕｎ，ＦａｎＪｉａｎｚｈｏｎｇ，ＺｈａｎｇＫｕｉ，ＺｈａｎｇＳｈａｏｍｉｎｇ，ＳｈｉＬｉｋａｉ（李...     

Improved Properties in Relation to Fine Precipitate Microstructures Tailored by Combinatorial Processes in an Al-Cu-Mg-Si Alloy

The 2xxx series Al alloys have been widely used in aerospace industry owing to their high strength, good plasticity and superior formability. To ensure a good control of shape, the quenched alloy sheets require a small pre-deformation before artificial aging. However, this pre-deformation considerably deteriorates the mechanical strength of the Al-3.0Cu-1.8Mg-0.5Si (wt%) alloys due to the formation of unfavorable large-sized precipitates at dislocations. To tackle this issue, we designed a pre-aging process prior to the pre-deformation. The thermal-mechanical treatment, involving pre-aging, pre-deformation and subsequent aging, markedly enhanced the ultimate tensile strength up to 521 MPa compared to that (448 MPa) of the alloy without pre-aging. Microstructure characterization revealed that the fine precipitates (~ 2 nm) with a uniform dispersion were promoted within the Al matrix, which in turn partly suppressed the formation of the unfavorable large-sized precipitate (~ 100 nm). Our findings provide a new clue for designing stronger Al alloys with age-hardenability.     

自然时效对6061铝合金锯齿形屈服的影响

对固溶处理淬火后自然时效时间不同的6061铝合金在室温下进行恒定应变率的拉伸试验,研究了自然时效对锯齿形屈服效应(Portevin-Le Chatelier,PLC)的影响。实验发现,材料强度、锯齿周期和临界应变三者在自然时效0~1 h期间均无明显变化,在自然时效超过1 h以后随自然时效时间延长而增大;锯齿幅值在自然时效0~2 h期间随自然时效时间延长而减小,在自然时效超过2 h后趋于稳定值。自然时效过程中,强化效果明显的β'相在自然时效时间1~2h之间开始形成并随自然时效时间线性增加。结合动态应变时效模型的分析结果与实验相符合,揭示了有强化效果的析出相对PLC效应的作用机制:具有强化效果的析出相含量增多将缩短可动位错的等待时间,使得可动位错更难被钉扎,从而导致锯齿周期和临界应变增大。分析结果还表明,该合金中溶质原子主要以体扩散方式向可动位错聚集从而实现对可动位错钉扎。     

喷射成形6061铝合金的热处理工艺

对喷射成形6061铝合金的热处理工艺进行研究,采用硬度测试、拉伸试验和透射电镜等研究固溶温度、时效温度和时效保温时间对合金显微组织和力学性能的影响规律。结果表明:随固溶温度的升高,合金硬度也随之升高,而其抗拉强度、屈服强度和断后伸长率则先增大后减小;合金硬度、抗拉强度和屈服强度随时效温度的升高先增大后减小,断后伸长率却一直减小;合金硬度、抗拉强度和屈服强度曲线随时效温保温时间的延长呈驼峰状变化,断后伸长率则变化不大,只在17 h时有所增大;喷射成形6061铝合金的最佳热处理工艺为530℃固溶1 h+175℃时效8 h。     

T6热处理对粉末触变成形技术制备Ti@(Al-Si-Ti)p/A356Al复合材料组织和性能的影响

本文采用粉末触变成形技术制备了由“芯-壳”结构粒子增强的A356Al复合材料,然后通过T6热处理进一步提高该复合材料的综合力学性能。研究结果表明,“芯-壳”结构增强体颗粒不仅能够提高复合材料的抗拉强度、屈服强度(增加率分别为18.0%和32.7%),而且使其(10.8%)具备与基体铝合金(11.3%)相当的塑性。在T6热处理过程中,随时效时间的延长,该复合材料的强度、硬度先增加(1-7h,即欠时效)后减小(9-12h,即过时效),在8h时达到最大值(即峰时效),此时复合材料的抗拉强度、屈服强度和硬度分别为325.4 MPa、254.4 MPa和104.0 HV,比热处理前分别提高了33.7%、74.0%和48.5%;峰时效延伸率为9.4%,与热处理前相比几乎没有下降。即经过T6热处理后,“芯-壳”结构增强体粒子能在提高复合材料强度的同时,最大程度地保留其良好的塑性。最后,通过对时效8h和12h的复合材料基体中析出相的尺寸、密度和类型的分析,对其强化机制进行了讨论。     

挤压态6061铝合金的力学性能及显微组织

对挤压态6061铝合金分别进行了固溶处理和时效处理,采用万能试验机测试了其力学性能,通过SEM和TEM表征了合金的微观组织,研究了不同热处理条件下挤压态6061铝合金的组织演变规律。结果表明:固溶和时效处理后的挤压态6061铝合金均表现出明显的力学性能各向异性,且时效处理能有效提升合金的强度;同时,经时效处理后的挤压态6061铝合金表现出应变速率敏感性,而固溶处理的挤压态6061铝合金则无明显的应变速率敏感性;固溶处理和时效处理的挤压态6061铝合金的晶粒形态为等轴晶,但是有大小两种晶粒尺寸等级,大晶粒尺寸可达200 μm,小晶粒尺寸则小于10 μm。固溶和时效处理的挤压态6061铝合金均由较强的{001}<100>立方织构和较弱的{011}<100>高斯织构组成,且种类和强度相同;拉伸变形后的6061铝合金出现了大量的位错堆积,而经时效处理的合金中均匀分布短棒状的析出相能有效阻碍位错的运动,提高材料的变形抗力。     

冷热循环对颗粒增强铝基复合材料微屈服行为的影响

采用微屈服强度测试、透射电镜和高分辨透射电镜分析,对经过不同冷热循环工艺处理后的颗粒增强铝基复合材料的微屈服行为进行了研究。结果表明,冷热循环次数虽然对颗粒增强铝基复合材料微屈服行为的宏观规律没有本质的影响,但是仍然影响颗粒增强铝基复合材料的微屈服行为。对球形颗粒而言,小应变量下的微屈服强度随冷热循环次数的增加而增高;但对棱形颗粒而言,循环次数的影响较为复杂。研究还表明,冷热循环次数影响颗粒增强铝基复合材料微屈服行为的主要原因是其位错组态和残余应力在不同的循环次数下有明显的不同。     

10%冷变形对7A85铝合金时效微观组织性能的影响

采用半连续铸造工艺制备了7A85铝合金铸锭、挤压工艺制备截面尺寸为50mm×300mm的挤压带板,并对挤压带板进行固溶处理、10%冷压缩处理以及120℃人工时效处理。通过TEM观察、力学性能测试等手段,研究了10%冷变形对7A85铝合金时效微观组织演变规律的影响。结果表明,固溶处理后,10%冷变形处理使合金中产生大量位错,从而提高了合金强度;时效初期,10%冷变形处理的7A85合金中析出相数量较未冷变形处理7A85合金明显增多,起到一定预时效作用;时效末期,10%冷变形处理的7A85铝合金析出相与位错数量均高于未冷变形处理的7A85铝合金,使得合金抗拉强度与屈服强度提升,而伸长率降低。     

Effect of pre-deformation on aging characteristics and mechanical properties of Mg-Gd-Nd-Zr alloy

The effect of plastic deformation prior to artificial aging on the aging characteristics and mechanical properties of a Mg-I lGd-2Nd-0.5Zr （mass fraction, %） alloy was investigated. After solution treatment at 525 ℃ for 4 h, the alloy was subjected to cold stretching deformation of 0%, 5% and 10%, respectively. The as-deformed specimens possess high density of dislocations and mechanical twins, which increase with elevated deformation. As compared with non-stretched alloy, the stretched alloy shows accelerated age-hardening response and slightly enhanced peak hardness when aged at 200 ℃. Comparison of the microstructures in undeformed and deformed specimens after 200 ℃, 24 h aging reveals that pre-deformation induces the heterogeneous nucleation of precipitations at dislocations and twin boundaries in addition to the homogeneous precipitation in the matrix. Room and high temperature tensile test results show that pre-deformation enhances the strength of the alloy, especially at room temperature, though the ductility declines. The improvement in strength of deformed and aged alloy is attributed to the combined strengthening effect of precipitates, deformation structures and grain boundaries.     

Effects of residual stress and dislocation on tensile deformation behavior of SiC_w/Al composites

1　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｒｅｓｉｄｕａｌｔｈｅｒｍａｌｓｔｒｅｓｓｃａｕｓｅｄｂｙｔｈｅｍｉｓ ｍａｔｃｈｏｆｃｏｅｆｆｉｃｉｅｎｔｓｏｆｔｈｅｒｍａｌｅｘｐａｎｓｉｏｎ (ＣＴＥ)ｂｅ ｔｗｅｅｎｒｅｉｎｆｏｒｃｅｍｅｎｔａｎｄｍａｔｒｉｘａｌｌｏｙａｎｄｈｉｇｈｄｅｎｓｉ ｔｙｄｉｓｌｏｃａｔｉｏｎｓｉｎｔｈｅｖｉｃｉｎｉｔｙｏｆｔｈｅｉｎｔｅｒｆａｃｅｓｒｅｓｕｌｔｅｄｆｒｏｍｔｈｅｒｅｌａｘａｔｉｏｎｏｆｒｅｓｉｄｕａｌｓｔｒｅｓｓｏｎｃｏｏｌｉｎｇｈａｖｅｇｒｅａｔｉｎｆｌｕｅｎｃ…     

半固态热等静压Al/B4C复合材料液相流动行为与致密化机理

铝基碳化硼复合材料是一种重要的中子吸收材料。为了制备具有更高密度的铝基碳化硼材料,研究采用粉末冶金半固态热等静压方法制备了含量为30%碳化硼的铝基碳化硼材料,采用WANCE100型材料力学性能试验机和SIRION200型扫描电镜研究了复合材料的力学性能及显微形貌。结果表明：半固态热等静压工艺可制备获得接近理论密度的Al/B4C复合材料;虽然Al/B4C材料抗拉强度可提升至约300Mpa,但过高碳化硼含量也使得该材料脆性特征十分明显;研究同时采用间接的方法观察到了半固态工艺过程中生成的液相,该液相不仅可改善碳化硼颗粒与铝基体的结合性,在高温高压下液相的流动还起到填充复合材料内部空隙的作用。半固态热等静压工艺过程中产生的液相是复合材料密度和机械性能提升的主要原因。     

流变轧制AZ91合金的热处理和组织性能调控

本文对连续流变轧制AZ91合金在热处理过程中的组织和力学性能演化进行了研究。热处理后两种析出相在基体中出现：一种是晶界处的非连续析出相,另一种是从过饱和基体中析出的小尺寸连续析出相。随着时效温度升高,原子扩散速度也随之提高,导致更多的析出相生成和长大。合金的维氏硬度和拉伸强度峰值在16小时时效后出现,而合金的延伸率随着时效时间的延长和时效温度的提高呈下降趋势。经过对实验结果的分析,适合提升合金综合力学性能的热处理制度为415°C固溶20小时加220°C时效16小时。经热处理后得到的维氏硬度、拉伸强度和延伸率分别为：99 HV,251 MPa和4.5%,各项性能均显著优于流变轧制态合金。相对于传统成型手段,流变轧制加热处理方法成型的AZ91合金展现了优异且均衡的综合力学性能。     

时效制度对6156铝合金力学性能及腐蚀性能的影响

通过常规拉伸、慢应变速率拉伸和晶间腐蚀实验研究了T6及双级时效处理对6156铝合金力学性能与腐蚀性能的影响,并采用透射电镜(TEM)观察了析出相特征。结果表明:6156合金在T6欠时效状态下晶内析出相主要为GP区,晶界无明显析出相;T6峰时效晶内析出相主要为β″相,出现少量的Q′相,晶界析出物呈连续分布,合金虽然具有最高强度,但晶间腐蚀严重,应力腐蚀敏感性最大;随时效时间延长,Q′相增多并逐渐粗化,晶界析出物粗大非连续分布;T78时效态晶内析出大量的Q′相,晶界析出相球化且析出相之间的间距增大,呈断续分布,无沉淀析出带(PFZ)变宽,因此相比T6态而言T78状态合金强度损失不大而耐蚀性得到明显提高。