The microstructure and mechanical properties of prolonged and lower temperature aged Fe–Ni–Mn–Mo–Ti–Cr maraging steel

In this study, the microstructure and mechanical properties of Fe–Ni–Mn–Mo–Ti–Cr maraging steel at low temperature and prolonged aging condition were investigated. Optical and scanning electron microscopy examinations, tensile and hardness tests were conducted to study the microstructure, aging behavior and mechanical properties of the cold‐rolled steel. The results showed that aging of cold rolled Fe–Ni–Mn–Mo–Ti–Cr maraging steel resulted in the formation of Mo rich and Ti rich Lave phase precipitates. Existence of many dislocation cores due to cold rolling and subsequently, low temperature aging caused to formation of uniform distribution of very fine precipitates. The presence of these precipitates increased the yield and ultimate tensile strengths but couldn't improve the uniform tensile ductility. This alloy showed ultra‐high fracture stress of about 1950 MPa with a negligible tensile elongation (about 2 %) at the peak aged condition. The fractographic studies indicated this alloy shows semi‐brittle fracture in the subsequent aging treatment.     

Aging impact on mechanical properties and microstructure of Al-6063

The impact of aging on the mechanical properties and microstructure of Al-6063 alloys were studied, using scanning and transmission electron microscopy, as well as tensile measurements. It was found that the 0.5% yield stress and the ultimate tensile strength increase at the beginning of the aging process, reach a maximum, and than decrease with increasing the aging duration. On the other hand, the uniform elongation, the total elongation, and the strain hardening factor decrease with increasing aging duration well after the material reaches the maximum strength (T6 conditions), reaches a minimum and than increase again. The final fracture area reduction also decreases to a minimum, which occurs simultaneously with the maximum of the ultimate tensile strength; then it increases with aging time. The final fracture area reduction is accompanied with morphology transition from transgranular shear rupture to a combination of transgranular shear rupture and intergranular dimpled structure. The intergranular rupture area increases with aging up to the minimum in the total elongation, and then decreases with aging duration. Aging is accompanied with the appearance of needle-like Mg₂Si precipitates except in Precipitation Free Zones (PFZ) that are adjacent to the grain boundaries. The PFZ size depends on the annealing temperature, while the morphology and density of the precipitates depend on the annealing duration. A correlation has been established between the PFZ and the measured mechanical properties and fracture morphology. The impact of the Mg/Si ratio on the mechanical properties is discussed.     

Effect of corrosion on mechanical behaviors of Mg-Zn-Zr alloy in simulated body fluid

The main purpose of this paper is to investigate the effect of corrosion on mechanical behaviors of the Mg-Zn-Zr alloy immersed in simulated body fluid （SBF） with different immersion times. The corrosion behavior of the materials in SBF was determined by immersion tests. The surfaces of the corroded alloys were examined by SEM. The tensile samples of the extruded Mg-2Zn-0.8Zr magnesium alloy were immersed in the SBF for 0, 4, 7, 10, 14, 21 and 28 d. The tensile mechanical behaviors of test samples were performed on an electronic tensile testing machine. SEM was used to observe the fracture morphology. It was found that with extension of the immersion time, the ultimate tensile strength （UTS）, yield strength （YS） and elongation （EL） of the Mg-2Zn-0.8Zr samples decreased rapidly at first and then decreased slowly. The main fracture mechanism of the alloy transformed from ductile fracture to cleavage fracture with the increasing immersion times, which can be attributed to stress concentration and embrittlement caused by pit corrosion.     

变质细化和热处理对挤压铸造成形A356铝合金构件性能的影响

用Al-10Sr变质剂和Al-5Ti-B细化剂处理A356铝合金熔体,并结合挤压铸造和T6热处理工艺,研究变质细化与热处理对A356铝合金挤压铸造件的组织和性能的影响规律。结果表明,随着Al-10Sr变质剂加入量的增加,共晶Si的形貌由片状和长杆状变为颗粒状和蠕虫状,α-Al的晶粒尺寸先减少后增大。当Al-10Sr的加入量(质量分数)为0.3%时,挤压铸造成形件的最优抗拉强度、屈服强度和延伸率分别为221.3 MPa、104.5 MPa和10.3%。Al-10Sr变质能提高形核率、细化α-Al晶粒尺寸和改变共晶硅形貌,使铸造件的力学性能提高。随着A-5Ti-B的增加,晶粒尺寸先降后增,力学性能先增后降。Al-5Ti-B的加入量为0.6%时,最优抗拉强度、屈服强度和延伸率分别为215.6 MPa、106.6 MPa和9.0%。T6热处理(固溶540℃/4 h+时效190℃/4 h)使屈服强度和抗拉强度显著提高和延伸率降低。经过0.6% 的Al-5Ti-B细化处理,T6处理挤压铸造件的最优的抗拉强度、屈服强度和延伸率分别为297.5 MPa、239.3 MPa和8.0%。共晶硅的球化和细化、成形件成分的均匀化以及Mg₂Si强化相在基体中弥散析出,是热处理后构件力学性能提高的主要原因。     

固溶前冷轧压下率对Cu-Ni-Si-Mg合金组织与性能的影响

为了优化Cu-Ni-Si-Mg合金的轧制工艺参数,利用光学显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)、能谱(EDS)和X射线衍射(XRD)等手段,对固溶前不同冷轧压下率下的Cu-Ni-Si-Mg合金时效态的组织性能及拉伸断口进行了分析.结果表明:随着冷轧压下率的增加,Cu-Ni-Si-Mg合金的平均晶粒尺寸逐渐增加,屈服强度、硬度和延伸率先增大后减小,抗拉强度表现为先增大,后在710 MPa左右波动,再减小的趋势;压下率从94%增加到96%,晶粒尺寸从12μm增加到52μm,而抗拉强度变化较小,归因于低压下时Cu-Ni-Si-Mg合金的细晶强化和时效强化占主导,而大压下时第二相粒子均匀的时效析出弥补了因晶粒粗大而造成的抗拉强度损失;压下率为93%时,合金的断裂为单一的韧性断裂,压下率为97%时,合金的断裂由韧性断裂和沿晶脆性断裂组成.     

Influence of retrogression and reaging on microstructure and properties of 8090 Al–Li alloy

Abstract

An investigation was made into the influence of a retrogression and reaging treatment on the microstructure, tensile properties, and stress corrosion cracking resistance of 8090 Al–Li alloy. The results show that retrogression of the material at 230°C for 40 min or 325°C for 1·5 min, and then reaging to the peak aged condition, can result in an improved combination of tensile strength and stress corrosion cracking resistance. Through retrogression and reaging treatment, the alloy almost achieves the strength of the peak aged state and the stress corrosion cracking resistance of the overaged state. Transmission electron microscopy indicates that the δ′ phase dissolves during retrogression and reprecipitates during reaging, thus increasing the strength. The T₂ phase precipitates and grows during both retrogression and reaging, which results in the increase of stress corrosion cracking resistance.

MST/1670     

Influence of pre-stretching and aging processes on comprehensive performance of aluminum alloy

The influence of pre-stretching and aging treatment on the mechanical properties and corrosion behavior of 7050 alloy were studied by tensile testing, potentiodynamic polarization, and intergranular corrosion (IGC) testing associated with optical microscopy (OM), scanning electron microscopy, and transmission electron microscopy. The results exhibit both strength and elongation of T6 are higher than T74. The strength of retrogression and re-aging (RRA) samples are equal to or even in excess of T6 sample, especially, the strength of RRA-60 sample increased by 5.7% at the sacrifice of its elongation. Both yield strength of T651 and RRA51-60 samples with 4% pre-stretching are enhanced while their elongation decreased too much. The fracture feature of T6 and T651 samples are majorly intergranular fracture, while the fracture mode of RRA samples are mainly transgranular fracture. The corrosion resistance of T74 could be significantly improved through IGC tests and electrochemical polarization tests. Also, RRA treatment leads to the most remarkable improvement. The reason is that the grain boundary precipitated phases become coarser, also the precipitation free zones of RRA-60 and T74 are wider than T6 aged sample. Furthermore, the corrosion resistance of pre-stretched samples are worse than those without pre-stretching.     

5083铝合金搅拌摩擦焊接头拉伸行为研究

目的 研究5083铝合金搅拌摩擦焊接（FSW）的组织、力学性能和拉伸应变,分析接头的拉伸行为。方法 采用数码相机、光学显微镜、电子扫描显微镜等表征分析方法,对焊缝的表面宏观成形、微观组织、断口形貌进行分析;利用拉伸机、三维数字动态散斑应变测量分析系统和显微维氏硬度计对接头的力学性能和拉伸应变进行测试。结果 不同焊接工艺参数下FSW接头的最低抗拉强度为305 MPa,断后延伸率达到了14%以上;焊核区拉伸应变沿板厚方向呈现上高下低和上宽下窄的不均匀梯度分布,发生了较大程度的变形强化,直到拉伸应力达到抗拉强度。断裂失效前300/120接头的最大拉伸应变在晶粒粗大的母材区,500/120和500/200接头的最大拉伸应变则位于晶粒尺寸差异较大的后退侧焊核区与热力影响区交界处。接头拉伸断口宏观上均为45°剪切韧性断裂,微观上均以韧窝韧性断裂为主,而高热输入500/120接头出现脆性断裂特征,其延伸率明显降低。结论 高热力耦合输入使铝合金FSW接头薄弱区发生转变,强韧性降低。     

The influence of post‐heat treatments on the tensile strength and surface hardness of selectively laser‐melted AlSi10Mg

To improve the mechanical properties of cast aluminium alloys several post‐heat treatments are known. However, these treatments cannot directly be transposed to additively via selective laser melting manufactured aluminium alloys, e. g., aluminium‐silicon‐magnesium (AlSi10Mg). Therefore, this study aims to determine suitable post‐heat treatments to optimise the mechanical properties of SLM‐built AlSi10Mg specimen. The influence of various post‐heat treatment conditions on the material characteristics was examined through hardness and tensile tests. The findings indicate that the Vickers hardness and ultimate tensile strength could not be improved via secondary precipitation hardening, whereas the fracture elongation shows a value which is distinctly higher than the values of a comparable cast alloy. Solution annealing at 525 °C reduces the hardness and the ultimate tensile strength by about 40 % and increases the fracture elongation three times. A subsequent precipitation hardening allows recovery of 80 % of the as‐built hardness, and 90 % of the previous ultimate tensile strength combined with maintaining an improved fracture elongation of about 35 % compared to the respective as‐fabricated condition.     

Adjustment of Aging Temperature for Reaching Superelasticity in Highly Ni-Rich Ti-51.5Ni NiTi Shape Memory Alloy

In this research, the effects of aging temperature on the phase transformation, mechanical properties, and superelasticity of Ti–51.5 at.% Ni alloy were investigated. For this purpose, samples were solution annealed and then aged at different temperatures ranging from 300 to 700°C. The results showed that the change of aging temperature has a great influence on the behavior of the alloy. Aging at 300 and 400°C led to the occurrence of the austenite to R phase (A ? R) transformation. By aging at these temperatures, the ultimate tensile strength and elongation did not change significantly compared to the solution annealed sample. Aging at 500 and 600°C led to the appearance of B19′ phase during cooling cycle of differential scanning calorimetry tests. Samples aged at 500 and 600°C showed the best mechanical properties, in comparison with the other aging temperatures. Maximum tensile strength of 1250 MPa and the elongation of 25% were obtained by aging at 500 and 600°C, respectively. Solution-annealed sample showed no superelastic property. Complete superelasticity was observed by aging at 400 and 500°C. The sample aged at 700°C showed the transformation behavior and mechanical properties similar to the solution annealed sample.     

Effects of creep age forming time on microstructure and high cyclic fatigue of 7075 aluminum alloy

In this paper, the hardness, ultimate tensile strength, yield strength, elongation E₁₀₀, S−N curves, and fatigue performance of 7075 aluminum alloy were obtained after aged at 170 °C for different times (10 h, 15 h, and 20 h). Additionally, the microstructure and fatigue fracture of the alloy were observed. The investigation results show that as the forming time increased, the hardness, ultimate tensile strength, and yield strength decreased, the elongation first decreased, then increased, and the fatigue limit increased. As the forming time increased, the metastable phase gradually transformed into a steady phase and coarsened, the width of precipitate free zone increased, and the width of the fatigue strip decreased. After creep age forming for 20 h, the precipitate free zone was the widest, approximately 100 nm.     

The effect of aging process on the microstructure and mechanical properties of a Cu–Be–Co–Ni alloy

The paper investigated the effect of two aging processes (i.e. normal aging and interrupted aging) on the microstructure and mechanical properties of a Cu–Be–Co–Ni alloy. The results of tensile and Kahn tear tests showed that the interrupted aging (IA) process could significantly improve the uniform elongation and plane stress fracture toughness with tiny decrease in ultimate tensile strength, when compared with the results from normal aging (NA) process. Under the scanning electron microscope, the fracture surface of samples treated by NA followed the intergranular fracture, while that of the samples treated by IA followed the transgranular fracture. The transmission electron microscope study revealed the differences between the microstructure of the alloy treated by NA and IA processes. After the NA process, the slender strip of γ′ precipitates aggregated at grain boundaries with a length of approximately 10 to 45 nm; the disk-shaped γ″ precipitates in the alloy treated by IA distributed homogenously throughout whole grains with a length of about 3 to 10 nm. The discussion of strengthening mechanisms demonstrated that the mechanism of precipitate shearing by dislocations made a contribution to the strengthening of the alloy treated by IA, while the Orowan mechanism was the dominant strengthening mechanism in the alloy treated by NA.     

Effect of boron on microstructure and mechanical properties of eutectic aluminum‐silicon alloy modified with phosphorus

In order to understand the effect of boron on the microstructure and mechanical properties of eutectic aluminum‐silicon alloy modified with phosphorus, complex modification of eutectic aluminum‐silicon alloy by aluminum‐3phosphorus and aluminum‐3boron was conducted. The results show that the area fraction of primary α‐aluminum in eutectic aluminum‐silicon alloy modified with aluminum‐3phosphorus increased first and then decreased with increasing amounts of aluminum‐3boron. The area fraction and the size of primary silicon decreased rapidly first and then stabilized. The morphology of eutectic silicon transformed from needle‐like into fine short rods or granules after complex modification with aluminum‐3phosphorus and aluminum‐3boron. The ultimate tensile strength of the alloy modified with 0.4 wt.% aluminum‐3phosphorus and 0.2 wt.% aluminum‐3boron increased by 18 %, compared with that of the eutectic aluminum‐silicon alloy modified with aluminum‐3phosphorus, while the elongation decreased by 5 %. It was concluded that the comprehensive mechanical properties of eutectic aluminum‐silicon alloy were improved.     

Sn对时效态ZM61镁合金高温力学性能的影响

利用金相显微镜(OM)、X射线衍射(XRD)、扫描电镜(SEM)和高温拉伸对时效态ZM61-xSn(x=0,6,8,10,质量分数/%,下同)合金的高温拉伸性能及断裂机制进行了研究。结果表明:ZM61-xSn(x=6,8,10)合金的物相由α-Mg,α-Mn,MgZn2,Mg2Sn相组成。添加Sn元素可有效细化ZM61合金组织,提高合金高温强度,但降低合金塑性。ZM61-xSn(x=6,8,10)合金在300℃下拉伸的抗拉强度分别为149,140,145MPa,较相同温度下拉伸的ZM61合金的抗拉强度分别提高了26%,17%,23%。ZM61-xSn(x=0,6,8,10)合金在300℃下拉伸的伸长率分别为39.95%,5.65%,7.01%和6.33%。拉伸温度对ZM61-xSn(x=6,8,10)合金的断裂机制产生显著影响。当拉伸温度低于220℃,合金为穿晶断裂;高于220℃时,合金变为沿晶断裂。     

Microstructural and mechanical behavior of SnCu–Ge solder alloy subjected to high temperature storage

This paper addresses the effect of high temperature storage on the microstructural and mechanical behavior of novel SnCu–Ge solder alloys. Eutectic Sn99.3Cu0.7 solder was micro-alloyed with the addition of minor Ge as an anti-oxidant and to improve the wetting performance of the alloy. The addition of Ge significantly reduced the aging degradation of the alloy. The ultimate tensile strength and yield stress dropped within first few days of aging and the fracture strain increased with aging. The corresponding microstructure changed after annealing at 125 °C for 3 months; the average grain size of the β-tin portions of the microstructure increased with aging and the imbedded IMC particles segregated along and/or within the grains. Based on growth kinetics and activation energy arguments, we suggest that the addition of Ge restricts the Cu diffusion into the alloy and inhibits the IMC growth.     

铸锻复合成形AZ91D摩托车发动机壳体热处理工艺研究

采用不同固溶和时效热处理工艺对液态铸锻双控成形AZ91D摩托车发动机壳体进行了热处理实验。结果表明:样品经过T4(415℃×9h,60℃水淬)处理后,合金的抗拉强度和延伸率最大,其值分别为239.7MPa,1.58%,较未热处理提高幅度分别为41.6%,79.9%。经T6(415℃×9h,60℃水淬+205℃×16h,空冷)处理后,样品显微组织中的第二相得到均化,在一定程度上强化了合金。未处理态、T4、T6状态下的拉伸试样断口形貌中均存在较多的韧窝,表明铸锻双控成形制件的塑性较好。T6(415℃×9h,60℃水淬)热处理后的拉伸试样断口形貌中韧窝最多,塑性最好。     

均匀化处理对Mg-13Gd-3.5Y-2Zn-0.5Zr镁合金组织和力学性能的影响

对Mg-13Gd-3.5Y-2Zn-0.5Zr镁合金铸锭进行均匀化处理,温度为505～525℃,时间为4～24h,并采用光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)和万能材料试验机等检测手段分析均匀化处理前后合金微观组织和力学性能的变化。结果表明:均匀化处理后,原始组织中网状分布共晶化合物转化成晶界处不连续分布的块状LPSO相,离散分布的方块状富稀土相溶解。力学性能测试显示,铸态镁合金的抗拉强度为172.9MPa,伸长率为1.8%,经过均匀化处理后合金的力学性能得到提高,在515℃/16h均匀化制度下,合金室温抗拉强度为212.3MPa,伸长率为3.1%;在200℃下抗拉强度为237.2MPa,伸长率为9.7%,性能达到最佳。断口扫描显示,铸态合金是以撕裂棱与解理台阶为主的解理脆性断裂,均匀化处理后的合金中出现小而浅的韧窝,但仍然是以解理台阶为主的准解理断裂,塑性提高有限,长程有序相可成为裂纹的萌生源。     

Al-7Sn-1.1Ni-Cu-0.2Ti轴承合金微观组织与力学性能

采用扫描电镜、能谱分析、金相显微镜与WDW-100KN万能拉伸试验机研究Al-7Sn-1.1Ni-Cu-0.2Ti轴承合金的微观组织与力学性能,结合盘-销式摩擦磨损试验机考察合金不同组织状态的润滑性能。结果表明:Al-7Sn-1.1Ni-Cu-0.2Ti合金凝固收缩率为1.13%,铸态抗拉强度、屈服强度、伸长率与布氏硬度分别为191,147MPa,15.6%与34.6HBS,随着低温时效与退火热处理过程的进行,抗拉强度略有上升,屈服强度保持不变,伸长率与布氏硬度均呈现出先上升后下降的变化趋势;沿晶界分布的共晶Sn相形貌受界面张力作用逐步由板片状与骨骼状转变为层片状与短棒状,部分吸热脱溶析出在晶界处形成空腔结构,初生α-Al基体平均晶粒尺寸为182μm。与铸态和340℃退火6h相比,经175℃时效10h后,摩擦因数降低了28.6%与78.6%,体积磨损量减少了157.1%与471.4%,断口形貌以沿晶断裂与韧窝断裂为主。     

低温对时效态TC4合金拉伸性能的影响

在77－300K温度范围内对不同时6效状态TC4合金进行拉伸试验，研究了低温对时效态合金拉伸性能的影响。时效温度取813天，时效时间分别为0．5h、7h、60h。试验结果表明：在室温下，时效0．5h合金与退火态合金相比强度明显提高，延伸率略有降低；时效时间大于0．5h，随时效时间的延长，合金的强度与延伸率均下降。随试验温度的降低，3种时效态合金的强度都单调增加，延伸率先是下降，但在77K时又略有升高，TEM观察表明，随着试验温度的降低，拉伸断口附近位错分布不均匀性增大。     

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。