胀形对2219铝合金环形件淬火残余应力的影响

利用ABAQUS有限元软件对2219铝合金环形件淬火过程及后续胀形过程中径向截面上残余应力的分布进行数值模拟,研究了胀形量对淬火残余应力消减率的影响。结果表明:淬火后环件的径向应力在上下端面呈压应力,在-106 MPa左右,在芯部应力值较小;周向应力和轴向应力均呈外部压应力、芯部拉应力的应力分布状态。胀形对环件的径向应力、周向应力和轴向应力均有显著的消减效果。胀形量在0.25%~4.00%范围内增加时,环形件的残余应力减小,周向应力和轴向应力的消减率都增大并趋于定值,且周向应力消减率的增大速度比轴向应力消减率的增大速度快。当胀形量<3%时,周向应力的消减率大于轴向应力的消减率,当胀形量>3%时,周向应力的消减率略小于轴向应力的消减率;当胀形量>2%时,周向应力和轴向应力的平均消减率>80%,环件的淬火残余应力得到很好的消减。     

Cu-Cr-Zr合金的低周疲劳行为

通过室温低周疲劳(LCF)试验研究了Cu-Cr-Zr合金的低周疲劳性能和循环变形行为,利用电子背散射衍射、透射电镜和扫描电镜分别分析了合金循环变形前后的微观结构和疲劳断口。结果表明:Cu-Cr-Zr合金的弹性应变幅、塑性应变幅与断裂时的循环周次之间的关系可分别用Basquin和Coffin-Manson公式表示。Cu-Cr-Zr合金在高外加总应变幅(Δε_t/2=0.6%)的疲劳变形后期会出现循环硬化现象,循环变形组织为位错墙、位错团簇、亚结构胞状组织的混合结构,并且观察到了孪晶的形成。此外,所选材料在外加总应变幅为0.4%时的疲劳断口呈现多疲劳源特征,疲劳裂纹扩展区中观察到了大量的撕裂棱、韧窝、以及犁沟。     

High cycle fatigue and fracture behavior of 2124-T851 aluminum alloy

The high cycle fatigue properties and fracture behavior of 2124-T851 aluminum alloy were investigated roundly, including the fatigue crack growth rate, fracture toughness and fatigue S--N curve. Furthermore, the fatigue crack growth rate was analyzed by fitting the curves. And the microstructure of the alloy was studied using by optical microscopy, transmission electron microscopy and X-ray diffractometry, scanning electron microscop1/2 The results show that the fatigue strength and the fracture toughness of 2124-T851 thick plate are 243 MPa and 29.6 MPa.m at room temperature and R=0. 1, respectively. At high cycle fatigue condition, the characteristics of fatigue facture were observed obviously. And the higher the stress amplitude, the wider the space between the fatigue striations, the faster the rate of fatigue crack developing and going into the intermittent fracture area and the greater the ratio between the intermittent fracture area and the whole fracture area.     

超声表面机械研磨处理对6061铝合金FSW接头疲劳行为的影响

利用超声表面机械研磨处理(USMGT)方法对6061-T6铝合金搅拌摩擦焊(FSW)接头进行了表面晶粒细化处理,采用光学显微镜、显微硬度仪、扫描电镜等测试手段,对接头组织、力学性能及疲劳性能进行了分析。结果表明,USMGT处理后焊接接头表面形成了包含大量细化晶粒的梯度细晶层,表面细晶层的形成使接头表面硬度得到提高;接头的宏观断裂位置在热机影响区(TMAZ)和热影响区(HAZ)之间,滚压处理强化试样表层,FSW接头内部TMAZ和HAZ之间出现的软化现象无法消除,相比其他区域,该部分依然是疲劳薄弱区,承受载荷时微观裂纹源萌生位置由表面向内部迁移;滚压处理会使表层引入残余压应力,从而使得接头的疲劳性能得到提高,当应力幅值为150 MPa时,USMGT后的接头疲劳寿命达到未处理的3．5倍。     

Tensile and fatigue properties of aluminum alloy sheet 6022

Tensile and fatigue tests were performed on aluminum alloy 6022 T4E29 and T6 sheet specimens in ambient air. The tensile and fatigue properties were compared with other commercial aluminum alloys. The results showed that 6022 alloy has high fatigue strength and good ductility with moderate tensile strength.     

Effect of tube size on electromagnetic tube bulging

The commercial finite code ANSYS was employed for the simulation of the electromagnetic tube bulging process. The finite element model and boundary conditions were thoroughly discussed. ANSYS/EMAG was used to model the time varying electromagnetic field in order to obtain the radial and axial magnetic pressure acting on the tube, The magnetic pressure was then used as boundary conditions to model the high velocity deformation of various length tube with ANSYS/LSDYNA. The time space distribution of magnetic pressure on various length tubes was presented. Effect of tube size on the distribution of radial magnetic pressure and axial magnetic pressure and high velocity deformafion were discussed. According to the radial magnetic pressure ratio of tube end to tube center and corresponding dimensionless length ratio of tube to coil, the free electromagnetic tube bulging was studied in classification. The calculated results show good agreements with practice.     

Effect of laser shock processing on residual stress and fatigue behavior of 6061-T651 aluminum alloy

Laser shock processing is a very new technique and an emerging modem process that generates compressive stresses much deeper into the surfaces of metals or alloys. A brief parametric study of the effect of laser parameters on fatigue behavior and residual stress state generated in 6061-T651 alloy specimens was summarized. Residual stress of 6061-T651 alloy was analyzed both before and after laser processing with multishocks. The material remains in compressive residual stress of approximate 1 mm in depth which is approximately 10 times deeper than that can be achieved with the conventional technique, and the maximal compressive residual stress at the surface of the sample is about -350MPa. Near the surface, yield strength and hardness are found to be increased by the laser shock. The ratio of fatigue crack initiation life for the laser-shocked to unshocked specimens is found to be 4.9 for specimens. The results clearly show that LSP is an effective surface treatment technique for improving the fatigue performance of aluminum alloys.     

铝合金搅拌摩擦点焊疲劳性能研究

研究了2mm厚的6082-T6铝合金搅拌摩擦点焊接头的疲劳性能。在最优的焊接工艺参数和良好的焊接接头的基础上,完成了点焊接头的疲劳实验,观察分析点焊接头薄弱环节的微观组织和疲劳断口的形貌,并测试接头显微硬度,得到了在一定范围内预测疲劳寿命的表达式。结果表明:疲劳裂纹在上下板间的接头根部起裂,在热影响区和热力影响区的交界处扩展直至断裂;微量元素形成的强化相在很大程度上影响点焊接头的疲劳性能;点焊接头的疲劳寿命随着应力强度因子的变小呈增大趋势。     

多轴载荷下ZL101铝合金的低周疲劳行为

研究不同等效应变幅下ZL101铝合金在多轴比例和非比例载荷下的低周疲劳行为,并用透射电镜观察合金的疲劳行为中的位错结构。结果表明：合金在两种加载方式下均表现为循环硬化;在非比例载荷下合金表现出附加强化,但程度不明显;合金的疲劳寿命随等效应变幅的增加而降低,合金在非比例加载下的疲劳寿命低于比例加载时的疲劳寿命。对位错结构的观察表明,随等效应变幅度的提高,合金的低周疲劳位错结构从交叉位错带转化为位错胞,合金在非比例加载下更易形成位错胞结构。     

Effect of pre-strain on fatigue crack growth of 2E 12 aluminum alloy

The influences of pre-strain on the mechanical property and fatigue crack growth of 2E12 aluminum alloy were evaluated by SEM, TEM, mechanical property and fatigue tests. The axial fatigue tests were conducted under a constant amplitude sinusoidal wave loading at stress ratio of 0.1 in laboratory air and salt fog at room temperature. The results show that the yield stress of pre strain material is higher than that of the material without undergoing pre-strain, but pre-strain can not make the increase of the growth rate of fatigue crack. Fatigue crack growth rates of the alloy in salt fog are higher than those in air. The increased fatigue crack growth of the alloy in a given environment and more brittle striations can be observed in salt fog.     

Effect of mould material on aluminum alloy ingot quality under low frequency electromagnetic casting

F or a semi-continuous aluminum casting process, it is essential to supply high quality aluminum alloy ingot without internal and outside defects. The use of electromagnetic fields to control the size and shape of grains has become one of the most promising methods [1-5] in many engineering applications and tends to be widespread in industries. The application of electromagnetic casting (EMC) technique for improving products quality has attracted a great deal of attention in recent years, and…     

焊缝几何特征对5A30铝合金焊接接头疲劳性能的影响

通过5A30铝合金不同焊缝形式、几何尺寸对接接头疲劳试验, 以及焊缝余高存在时焊趾处的应力集中系数的测定和理论计算, 研究了焊缝几何特征对铝合金焊接接头疲劳性能的影响. 结果表明: 单面焊双面成型和双面焊对接接头的疲劳性能相当, 在循环次数为(1.7～1.8)×106时, 疲劳强度约为100.MPa; 焊缝余高的存在使接头的疲劳性能明显降低, 增大焊缝余高, 接头疲劳性能显著下降, 去除余高, 则可使接头的疲劳寿命提高2～3倍; 厚度为4.mm板材对接接头, 焊缝余高为1～2.mm时, 焊趾处的应力集中系数较其他部位增大50%左右, 焊缝余高大于3.mm, 焊趾处的应力集中系数可超过1.70.     

5052铝合金交流脉冲等离子弧焊接工艺

采用交流等离子焊接方法,使用焊材ER5356对8 mm 5052铝合金进行了等离子弧立向上焊接试验。通过合理的设计焊接工艺和严格控制焊接关键因素,解决了5052铝合金焊接性的问题。结果表明,交流等离子弧焊接方法适用于5052铝合金的焊接,根据标准对焊接接头进行力学性能检测、X射线检测与焊接接头金相分析。结果表明,焊接接头弯曲和拉伸性能符合检测标准要求,冲击吸收能量在15 ℃条件下均大于19 J;焊缝无气孔、夹渣等缺陷,焊缝中组织基体为α(Al)固溶体。     

内外压复合作用下5A02铝合金管材的硬化行为

为了研究管材在内外压复合作用下的硬化行为,在中间自由胀形区为椭圆形轮廓线的假设条件下,理论推导得到内外压复合作用下管材的应力/应变分析模型;再利用薄壁5A02-O铝合金管材在研制的内外压复合成形实验装置上进行外压为85 MPa(1.0σs)的实验研究,得到5A02铝合金管材在内外压复合作用下的应力-应变曲线。结果表明:5A02铝合金管材在内外压复合作用下进行胀形时,其胀形区轮廓形状依然可以准确地用椭圆函数进行拟合,且最高点处壁厚与胀形高度符合线性关系;由内外压复合胀形得到的应力-应变曲线的硬化指数n值为0.274,低于单向拉伸时得到的n值(0.304)。     

6066铝合金弹体破片形成机理

以挤压及热处理 (T6态 )工艺制备 6 0 6 6铝合金圆管型模拟炸弹 ,进行了力学性能测试、砂坑中爆破试验及扫描电镜断口形貌观察。研究结果表明 :随着应变速率的提高 ,6 0 6 6铝合金强度升高 ,塑性下降 ,断口从韧性向脆性转变。爆破破片断口形貌由拉伸断裂、剪切断裂及其过渡区组成 ,但以拉伸断裂为主。6 0 6 6铝合金作为弹体材料密度小、装药量大、爆轰力大 ,故而破片率及破片初速大 ,杀伤力大。通过破片的断裂特征 ,分析了与材料动态断裂行为相关的形貌特征 ,研究了该弹体材料的膨胀断裂行为     

残余应力对高速列车A7N01铝合金焊接接头疲劳行为的影响

研究了残余应力在疲劳加载过程中的应力松弛行为,采用预拉伸、表面喷丸等表面预制残余应力的方法预制了表面残余应力,并研究了焊接接头的疲劳性能. 结果表明,在经过1×105周次循环载荷后,各个部位残余应力发生较大松弛,在经过2×105周次后,应力松弛较1×105周次时松弛幅度降低. 在2×105周次后,应力松弛不再明显,最终残余应力分布在拉应力20～40 MPa之间. 当引入残余应力后,各种条件下的实际应力循环比发生了明显的变化,当应力比R≥0时,随着R的增大,平均应力增大,试样的疲劳周次显著下降. 残余压应力会使裂纹萌生的周期缩短,同时加快疲劳裂纹扩展速率.     

A356铸造铝合金的疲劳裂纹萌生及短裂纹扩展研究

研究了A356-T6铸造铝合金的缺口疲劳裂纹萌生与早期扩展行为及机制.结果表明,热等静压试样的疲劳抗力优于非热等静压试样.对于钝缺口试样,疲劳裂纹萌生于缺口根部附近的多个平面,最终哪个裂纹源扩展成主裂纹取决于局部微观组织.对于缺口几何形状不同的热等静压和非热等静压疲劳试样,在疲劳过程中,不管是在高应力状态下,还是在低应力状态下,都出现了铝基体的循环塑性变形和共晶硅粒子断裂导致疲劳裂纹萌生.对于非热等静压试样,铸造缩孔在构件的疲劳过程中起着重要作用,但即使缺口根部存在较大尺度的铸造缩孔,导致了疲劳裂纹萌生,但也同时观察到疲劳裂纹从共晶硅粒子、金属间化合物、铝基体的滑移带和铁基金属间化合物等处萌生.对于脆性的A356铸造铝合金可采用修正的断裂力学参量ΔKn、局部应力范围Δσ或局部应变幅Δε/2作为控制参量来表征疲劳裂纹萌生行为,而缺口有效应力强度因子范围ΔKneff和ΔJs参量可用来表征缺口场中短裂纹扩展行为.     

6005A铝合金焊接接头预腐蚀对其疲劳性能的影响

6005A铝合金广泛用于高速列车的生产。通过对4 mm厚6005A铝合金焊接接头进行预腐蚀试验及疲劳性能测试,研究不同预腐蚀等级下6005A铝合金焊接接头的疲劳寿命及预腐蚀对焊接接头疲劳强度的影响。结果表明,6005A铝合金焊接接头经预腐蚀后,腐蚀最严重的为熔合线,其次为母材,焊缝腐蚀程度最轻;与未腐蚀试样相比,预腐蚀试样的疲劳极限有一定降低;预腐蚀后焊接接头断裂均在熔合线;断口疲劳源区可发现类解理河流、台阶花样及擦伤痕迹,疲劳扩展区发现明显疲劳条带。