电火花工艺参数对7075铝合金板毛化形貌影响

为了研究电火花毛化7075铝合金工艺,采用铜电极在电火花成型机上对7075铝合金板进行电火花毛化正交试验,研究电火花的峰值电流ie、脉冲宽度ti和脉冲间隔t0三个试验因子对毛化表面形貌(粗糙度Ra、凹坑直径D和单位长度凹坑数Pe)的影响。结果表明,峰值电流和脉冲宽度是影响7075铝合金毛化表面形貌的主要因素,而脉冲间隔对毛化表面质量影响不大。     

铝合金覆层板胀形过程及成形性能（英文）

基于幂硬化材料模型,分析覆板材料强度系数K、加工硬化指数n及厚度t对成形板材胀形性能的影响,并以铝合金LF21为研究对象,选择不同厚度及性能的覆板进行了粘性介质压力胀形实验,从覆板材料性能及厚度等方面对板材胀形试件几何形状、壁厚分布规律及极限胀形高度等方面验证了分析结果的准确性。研究结果表明:覆板成形时,选择强度系数K较高、加工硬化指数n值较大及适当厚度的覆板有助于板材成形性能的提高。     

变压边力对铝合金板冲压成形的影响研究

通过数值模拟和实验,研究了变压边力对铝合金板成形过程中应变路径的变化规律,基于MK法研究应变路径的变化对铝合金板成形极限(FLC)的影响,通过比较不同随时间变化的压边力对铝合金成形极限的影响,揭示变压边力改善铝合金板冲压成形性能的机理。实验和数值模拟结果表明,变压边力改善铝合金板成形性能的主要原因是变压边力对应变路径的影响,对杯形拉深来说,渐增型随时间变化的变压边力可以改善铝合金板的成形性能。     

基于Pamstamp的5182铝合金发动机罩内板冲压数值模拟

通过三个方向的单向拉伸试验及成形极限试验,获得了5182铝合金的材料性能数据,建立了5182铝合金成形用材料模型。基于Pamstamp软件,建立了铝合金发动机罩内板的冲压数值模型,获得了压边力为1 000 k N,摩擦因数为0. 12时铝合金发动机罩内板的成形性能。研究了工艺参数对铝合金发动机罩内板成形的影响,获得了压边力、摩擦因数对其减薄率和增厚率的影响规律。通过铝合金发动机罩内板冲压试验,验证了数值模拟的可靠性。     

5083铝合金板在不同温度下的伸长率及拉胀成形极限

通过在不同变形温度和变形速率下进行单向拉伸实验,得到5083铝合金板材的伸长率变化规律,变形速率为1 mm·min~(-1)、变形温度为350℃时,伸长率达到最大值131%。运用Dynaform模拟5083铝合金板材在不同温度下的温成形实验,并利用自行设计的温成形实验装置进行实验验证,得到了不同温度下数值模拟和物理实验的成形极限图,对比发现:随着温度的增加,铝合金板的胀形极限增加,在300℃时材料的成形极限最高。最后,模拟了5083铝合金板材在不同温度下的温拉深破裂实验,并利用铝合金板温成形实验装置进行实验验证,得到了不同温度下的板料拉深极限直径,计算出不同温度下的极限拉深系数。研究表明,极限拉深系数随着温度的增加呈高-低-高的变化规律,5083铝合金板的温成形最佳温度为250℃。     

激光冲击工艺对6061-T6铝合金侵蚀性能的影响（英文）

采用激光冲击工艺处理6061-T6铝合金,研究了二氧化硅砂对其侵蚀磨损性能的影响。其中冲击角为15°、30°、60°、90°,粒子速率为37和58 m/s,采用两种激光进行辐照。采用3D轮廓测量法表征了侵蚀形貌,并采用SEM研究其侵蚀机理。结果表明,冲击角较小时,侵蚀磨损最大。侵蚀强度和侵蚀机理不受激光冲击工艺的影响,而与侵蚀的高应变速率有关。侵蚀图之间的差异是由于激光冲击工艺造成的表面粗糙度不同。最大质量损失和最大侵蚀深度分别出现在冲击角度为15°和30°时。最后,发现了明显的侵蚀机理的转移,从低角度的切割机制到90°时的凹坑形成。     

激光冲击波传播特性对E690钢表面微凹坑动态塑性变形的影响

为研究激光冲击次数以及多次冲击过程中冲击波的传播特性对微凹坑动态塑性变形的影响,利用ABAQUS有限元软件分析了应力波在E690高强钢中的传播规律及微凹坑动态塑性应变规律,并设计试验验证了仿真的准确性。结果表明,由冲击压力引起的应力波在材料深度方向的衰减呈现先快后慢的特性,第3次和第4次冲击过程中应力波的衰减速度基本接近。受冲击波动态传播过程中表面波与纵波协同作用的影响,微凹坑表面塑性变形深度整体呈现沿光斑中心径向向四周递减,对比冲击1~4次后微凹坑深度方向塑性变形的测试结果与模拟结果,最大误差为4.80%,仿真模型准确可靠。同时,多次冲击后表面硬度增加趋势变缓,4次冲击后微凹坑表面出现硬化饱和现象。     

铝合金车轮的有限元强度分析及试验验证

对几百款铝合金车轮的冲击试验、弯曲疲劳试验和径向疲劳试验进行了有限元分析,并通过台架试验进行验证对比,研究总结出了低压铸造铝合金车轮有限元强度分析的方法及边界条件,为铝合金车轮的结构设计和安全使用提供了参考。     

材料循环软化性能对安定极限载荷的影响

针对材料的循环软化性能对结构安定极限载荷的影响展开研究。以机械结构中常用的具有循环软化性能的Q235材料为研究对象,通过拉伸试验和循环加载试验进行相应的力学性能测试,进而以安定性分析研究中带中心圆孔方板这一典型结构为例,基于上述试验所测定的材料性能参数,对其受均布拉伸载荷循环作用情况下的安定极限载荷进行了有限元分析,并对方板进行了安定极限载荷的物理试验测试。结果显示,通过拉伸试验及循环加载试验所测得的Q235的屈服强度分别为293. 1和251. 3 MPa,采用以循环加载试验测定的屈服强度得到的方板的安定极限载荷,较采用拉伸试验的减小约14. 1%,且更接近试验测试结果。     

3A21铝合金搅拌摩擦焊接头力学性能研究

采用搅拌摩擦焊方法对厚度为6 mm的3A21铝合金板进行对接焊,研究了其接头的拉伸性能、弯曲性能、冲击性能和显微硬度。结果表明,焊接接头抗拉强度134MPa,接头强度系数为86%;接头弯曲性能良好;接头焊核区冲击韧度最好;焊接区显微硬度值较低,发生了软化。     

Impact resistance of lightweight hybrid structures for gas turbine engine fan containment applications

The ballistic impact resistance of hybrid composite sandwich structures was evaluated with the ultimate goal of developing new materials or structures for potential gas turbine engine, fan containment applications. The sandwich structures investigated consisted of GLARE-5 (Aviation Equipment, Inc., Costa Mesa, CA) laminates as face sheets with lightweight cellular metallic materials such as honeycomb, foam, and lattice block as a core material. The impact resistance of these hybrid sandwich structures was compared with GLARE-5 laminates and 2024-T3 Al sheets, which were tested as a function of areal weight (material thickness). The GLARE-5 laminates exhibited comparable impact properties to that of 2024-T3 Al at low areal weights, even though there were significant differences in the static tensile properties of these materials. The GLARE-5, however, did have a greater ballistic limit than straight aluminum sheet at higher areal weights. Furthermore, there is up to a 25% advantage in ballistic limit for the GLARE-5/foam sandwich structures compared with straight 2024-T3 Al. But no advantage in ballistic limit was observed between any of the hybrid sandwich structures and thicker versions of GLARE-5. Recommendations for future work are provided, based on these preliminary data.     

新淬火铝合金板材成形回弹试验与数值模拟

研究了铝合金2024-T3板料在新淬火状态下的成形过程.首先测量了2024-T3板材在新淬火状态下的力学性能,与原始状态性能比较发现,屈服强度和抗拉强度降低,延伸率增大,韧性增加.基于数值模拟方法模拟了橡皮成形过程的回弹规律,对翼肋零件的翻边回弹进行了数值模拟,并通过试验进行了比较.结果表明,数值模拟与试验结果吻合较好,模拟与试验间的偏差足板料发生加工硬化所导致的.因而,通过模拟可以得到考虑了回弹的模具形状,从而修正模具,使回弹后形状达到没计的精度.数值模拟与试验比较表明该方法是可行性的.     

Synergistic effect of pH and oxalate concentration on corrosion of aluminium alloy 2024-T3

This work aims at obtaining comprehensive information on the corrosion behaviour of AA2024-T3 in oxalic acid solutions under different concentrations (0.007–0.2?M) and pH (2–6). Various tests to characterise the corrosion behaviour are performed, including weight loss and electrochemical tests. Coupon surfaces are examined using infinite-focus microscopy, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, Raman spectroscopy and diffuse reflectance infrared Fourier transform spectroscopy. Corrosion rates, anodic and cathodic reaction kinetics are detailed to provide a fundamental understanding of the electrochemical behaviour of AA2024-T3 as a function of pH and oxalate concentration. The synergistic effect of pH and oxalate concentration on corrosion of AA2024-T3 is evaluated for both AA2024-T3 matrix and main intermetallics (i.e. Al–Cu–Mg and Al–Cu–Fe–Mn) and the electrochemical behaviour of each constituent element in AA2024-T3 is systematically studied.     

Slow strain rate testing of high-strength aluminium alloy plate in an aqueous solution of 3% NaCl + 0.3% H2O2

The stress corrosion cracking (SCC) behaviour of aluminium alloy plate materials was investigated in the short transverse direction using the slow strain rate (SSR) testing technique. The synthetic environment used was an aqueous solution of 3% NaCl + 0.3% H₂O₂. Reference tests under constant deformation and alternate immersion conditions according to ASTM G44 were performed, too. Both static and dynamic loading tests indicate high SCC susceptibility with the alloys 2024-T351, 2091-T8X51, 7050 T651 and 7475-T651. For the alloy 8090-T8171, a low SCC resistance is found in the alternate immersion tests, whereas a rather moderate sensitivity is observed performing SSR tests. The SSR testing technique fails to indicate the SCC sensitivity of the more resistant alloys 2024-T851 and 7050-T7651. As demonstrated by pre-exposure tests, the reduction of fracture energy observed with the latter alloys as well as with the immune alloys 7050-T7351 and 7475-T7351 is caused by pitting and intergranular corrosion. Using an aqueous solution of 3% NaCl + 0.3% H₂O₂, the SSR testing technique is a useful rapid method to screen wrought aluminium alloys which are quite sensitive to environmentally assisted cracking. Because chloride-peroxide solutions are also conducive to corrosion processes independent of stress, pre exposure tests are required to be incorporated into such sorting tests.     

Semi-solid near-net shape rheocasting of heat treatable wrought aluminum alloys

Flexibility of the CSIR-RCS, induction stirring with simultaneous air cooling process, in combination with high pressure die casting is successfully demonstrated by semi-solid rheocasting of plates performed on commercial 2024, 6082 and 7075 wrought aluminum alloys. Tensile properties were measured for the above mentioned rheocast wrought aluminum alloys in the T6 condition. The results showed that tensile properties were close to or even in some cases exceeded the minimum specifications. The yield strength and elongation of rheocast 2024-T6 exceeded the minimum requirements of the wrought alloy in the T6 condition but the ultimate tensile strength achieved only 90% of the specification because the Mg content of the starting alloy was below the commercial alloy specification. The strengths of rheocast 6082-T6 exceeded all of the wrought alloy T6 strength targets but the elongation only managed 36% of the required minimum due to porosity, caused by incipient melting during solution heat treatment, and the presence of fine intermetallic needles in the eutectic. The yield strength of rheocast 7075 exceeded the required one and the ultimate tensile strength also managed 97% of the specification; while the elongation only reached 46% of the minimum requirement also due to incipient melting porosity caused during the solution heat treatment process.     

Investigation of the SCC behaviour of alloy 2024 using the slow strain rate technique

The stress corrosion cracking (SCC) behaviour of 2024 plate in T351 and T851 tempers was investigated in short transverse direction performing accelerated tests under constant deformation, constant load and slow strain rate conditions. Corrosive media used were: aqueous 3.5% NaCl solution, an aqueous solution of 2% NaCl + 0.5% Na₂CrO₄ at pH 3 (according to LN 65666), an aqueous solution of 3% NaCl + 0.3% H₂O₂, and substitute ocean water according to ASTM D1141. Alternate immersion tests in 3.5% NaCl solution indicated the low SCC resistance of the alloy 2024-T351 as well as the improved SCC behaviour due to aging to T851 condition. Similar results were obtained from constant load tests under permanent immersion conditions in the acidified chloride-chromate solution, in 3% NaCl solution with peroxide, and in substitute ocean water, whereas no SCC failure was observed with specimens which were permanently immersed in 3.5% NaCl solution. Using the slow strain rate method, 3% NaCl + 0.3% H₂O₂ and substitute ocean water were found to be effective synthetic environments. The other two electrolytes did not promote severe stress corrosion cracking with alloy 2024-T351. The SCC behaviour of 2024-T851 was difficult to determine employing the slow strain rate technique. Large scatter in data, observed even in inert environment, and the low elongation of the aged material, exacerbated by a further degradation of ductility due to pitting and intergranular corrosion, precluded an evaluation.     

Prior corrosion and fatigue of 2024-T3 aluminum alloy

Pit-to-crack transition experiments were conducted on two thicknesses of 2024-T3 aluminum alloy. Specimens were corroded using a 15:1 ratio of 3.5% sodium chloride solution and hydrogen peroxide prior to fatigue loading. Cracks originating from corrosion pits were visually investigated using various microscopy techniques in order to gain insight into the pit-to-crack transition process.All pre-corroded specimens in this study fractured from cracks associated with pitting. Pit-to-crack transition was successfully observed using digital video techniques. The more aggressively corroded 2024-T3-4.064 mm specimens experienced more of an overall fatigue life reduction than 2024-T3-1.600 mm specimens. Results indicated that quantities such as pit surface area and surrounding pit proximity are as important as pit depth in determining when and where a crack will form.     

Aluminum alloy 6013 sheet for new U.S. Navy aircraft

The recently developed aluminum alloy 6013-T6 has been selected for the fuselage skin and other applications on the U.S. Navy’s P-7A airplane, in place of the traditional 2024-T3 clad sheet. Alloy 6013-T6 is naturally corrosion resistant, like the well-established alloy 6061, and hence is used unclad. Its fatigue strength, fatigue crack growth and fracture toughness compare favorably with 2024-T3. Replacement of alloy 2024 with alloy 6013 also reduces manufacturing costs for formed parts, because 6013 is readily formed in the T4 temper, then simply aged to T6, thus avoiding the costly heat treatments and straightening required for alloy 2024.     

基于非线性超声调制频谱识别铝合金板材的疲劳裂纹

基于非线性超声调制频谱法,对航空铝合金板材中的疲劳裂纹识别进行研究;以两个不同频率的超声兰姆波为激励信号.依靠超声换能器、波形发生器和激光测振仪等,对含有疲劳裂纹和无损伤的2024-T351铝合金薄板试样进行对比实验;分别采用时域、频域和时频域联合法分析非线性超声波在铝合金薄板试样中传播的响应信号.结果表明:非线性声学特征即调制频谱及三阶谐波可作为识别2024-T351铝合金板材介质中疲劳裂纹的判据,通过对试样表面进行扫描,建立调制频谱的峰值幅度与位移的关系,据此可确定样板中疲劳裂纹的位置和轮廓,这为航空铝合金板材疲劳裂纹的识别提供更多技术支撑.     

应变强化对钢板局部凹痕抗力影响研究

随着车身轻量化要求的日益提高,抗凹性作为汽车外覆盖件选择的重要指标越来越受到关注.本文以4种不同屈服强度的钢板为研究对象,开展了不同单拉预变形条件下板材局部凹痕抗力试验.结果显示,单拉预变形过程的应变强化将显著提高钢板的强度和局部凹痕抗力.随着钢板屈服强度的提高,产生一定深度永久凹痕变形所需的载荷也增大,抗凹陷能力得到进一步加强.对于大型汽车外覆盖件,冲压工艺过程的应变强化将提高其抗凹性.