电阻点焊接头的组织和力学性能是影响焊接质量和性能的关键因素[5,6]。国内外学者针对这一问题进行了大量研究：1、用实验测量和数值模拟等方法研究焊接过程中温度场的变化规律,并分析相应的相变行为[7]。易荣涛等[8]基于热弹塑性理论和线性混合法则,将数值模拟与实验相结合研究了超高强度热成形钢的相变和热膨胀系数对点焊接头应力场的影响。Yuta Funabiki等[9]研究了Fe和Al合金电阻点焊过程中熔化区的温度场和对流场的变化，施加磁场增大对流驱动力，使焊接界面层形成较均匀的温度场提高接头的强度。使用金相分析、X射线衍射等手段研究不同焊接工艺接头的组织形态、相组成,并分析其与力学性能的关系[10]。周国荣[11]通过数值模拟与金相分析，进行了分析和讨论超高强度热成形钢的焊接接头中不同区域温度场的变化和不同区域的组织形态。岑耀东等[12]利用多种材料组织和性能分析手段，研究了等厚TRIP980高强钢/SPCC低碳钢板与低碳钢接头的性能和纤维组织，发现近熔核侧的硬相马氏体组织是影响接头力学性能的关键因素。2、用拉伸和剪切实验等手段评价焊接接头的强度、断裂特性等力学性能,并分析其与接头组织的关系[13,14]。陈怀宁等[15,16]研究了不锈钢电阻点焊接头在不同温度、不同应力比和腐蚀条件下的疲劳性能对比和开裂机理，还基于有限元仿真模拟和残余应力分析得到了5083/7N01铝合金电阻点焊接头不同区域残余应力的分布规律。罗震等[17]建立了不同焊接工艺2219/5A06铝合金电阻点焊接头的熔核信息数据库，引入人工智能和深度学习的方式，预测不同工艺下的电阻点焊接头质量，又提出了一种结合主成分分析和相关性分析的多信号融合方法优化反向传播神经网络(BPNN)模型，提高了模型的预测准确率。3、针对不同材料和结构,研究焊接电流、焊接时间、电极力等工艺参数对接头性能的影响,并进行优化设计。郭太吉等[18]研究了不同焊接工艺的301L不锈钢板间密封胶对电阻点焊接头的熔核直径、熔透率、缩孔和力学性能的影响。孙大千等[19]研究了6061-T6铝合金-SUS301L不锈钢异种金属的典型铝/钢界面双层结构电阻点焊接头的断裂模式，以及焊接电极形状对接头熔核直径、熔透率和力学性能的影响。成家龙等[20]在AZ31B/不锈钢板间添加FeCoNiCrMn颗粒将点焊接头的拉剪载荷提高了397%。Hamed Pashazadeh等[21]以焊接时间、焊接电流和焊接压力为人工神经网络输入端、以熔核尺寸作为输出端并基于多目标遗传算法和数据统计，预测最优电阻点焊熔核尺寸下的点焊工艺参数。本文参照焊接车体工艺，研究不锈钢电阻点焊接头的微观组织组织、拉剪性能和开裂机理。
1 实验方法
实验用母材是加工强化的SUS301L-HT奥氏体不锈钢，其化学成分列于表1。焊接的接头是不同板厚组合的双层板。
表1 母材化学的成分
Table 1
| C | Si | Mn | P | S | Ni | Cr | N | Fe |
|---|---|---|---|---|---|---|---|---|
| 0.03 | 1.00 | 2.00 | 0.045 | 0.03 | 7.10 | 17.70 | 0.2 | Bal. |
使用松下YR-500电阻点焊焊接机，用双面单点形式制备点焊接头，使用直径为26 mm的电极C型夹钳，电极材料是铬锆铜合金(CuCrZr)，电极形状为圆锥形(R75)，已经过预压、保压和泄压，焊接工艺如图1所示。
图1
接头熔核区域的成像检测结果如图2所示，成像的深蓝色区域a为检测区外，红色区域b检测区内的板间隙成像，浅蓝色区域c为熔核形貌成像，浅红色区域d为熔核内缺陷成像。对比无损检测结果和实际熔核形貌可见，焊点熔核的尺寸和内部缺陷具有一致性。
图2
图2
电阻点焊接头超声波检测结果与实际熔核对比
Fig.2
Comparison between ultrasonic testing results of resistance spot welding joints and actual nuggets; (a) ultrasonic testing results; (b) actual nuggets
用线切割机将超声波成像检测后的接头沿焊点中心线截取长度为20 mm宽度为10 mm的试样，板厚组合为3 mm + 4 mm双层板。为了保证接头的宏观形貌和显微组织观察的准确性，对接头表面进行了机械清理以去除污物、氧化物等杂质。接头试样，如图3所示。使用不同粗糙度的砂纸用磨抛机打磨后，用Axiocam 105 color体视镜观察接头横截面的宏观形貌。使用Leco MicrochardnessTester LM247 AT仪器测试和分析接头横截面的硬度，如图5所示。使用中国科学院金属研究所研发的IBIS (Instrumented ball indentation system)力学性能表征系统，分别表征同一点焊接头的熔核区、热影响区和母材区的微区力学性能 [24]，用球形压头对探测区进行加载和卸载，快速测量金属材料表面的力学性能。
图3
图4
图5
图5
电阻点焊接头横截面宏观形貌
Fig.5
Macroscopic morphology diagram of resistance point welding joint cross-section
为了模拟实际运行过程中受力情况，使用如图4所示的拉剪试样对不同板厚组合的双层板点焊接头进行拉剪试验，实验标准参照JIS Z3136。使用GOTECH AL-7000-LA20万能实验机进行拉伸实验，最大拉力设置为200 kN，拉伸速度为0.5 mm/min。用FEI QUANTA 450扫描电镜观察拉剪断口的微观形貌。
2 结果和讨论
2.1 接头的宏观形貌和显微组织
图5给出了从接头的宏观形貌中测出接头的熔核形貌、内部缺陷、熔核直径、压痕深度和熔透率等参量。从图5可见接头的3个组织和性能不同的典型区域熔核区(Nugget zone，NZ)、热影响区(Heat affected zone，HAZ)、母材区(Base metal zone，BMZ)和板间熔核结合面(Nugget combined surface，NCS)。由于焊接工艺或散热不均匀，清晰可见熔核内中心区域的孔洞。在5 V电压下用10%草酸和90%水溶液电化学腐蚀42 s后，可得低倍组织及显微组织。如图6d所示，接头的熔核区稍向4 mm厚的下层板偏移。其原因是，双层板接头的板厚不一致，其本质原因是厚度不等双层板使焊接时4 mm板侧电阻大，产生的热量多而散热少。板厚的差距更大时，这种熔核偏移更显著。
图6
图6
点焊接头的低倍组织和显微组织
Fig.6
Macroscopic morphology and microstructure of resistance spot welded joints(a) base metal zone (b) heat affected zone (c) corona bond zone (d) macroscopic morphology of resistance spot welded joints (e) the center of nugget (f) shrink zone (g) the side of nugget
电阻点焊的原理是使工件结合面的温度高于熔核区金属熔点，电阻产生的热量使母材迅速熔化，在后续的冷却过程中在熔核心部和边部形成不同的微观组织。停止加热后，液态金属先从熔核边界开始结晶形成随着热流方向排布的柱状晶组织，如图6g所示。熔核心部的组织则为等轴枝晶，如图8e所示。母材区距离熔核区较远，在焊接过程中峰值温度小于液相线温度，微观组织未发生变化，主要组织为奥氏体和少量沿着轧制线方向的马氏体组织，如图6a所示。位于熔核周边区域的热影响区在焊接过程中同时受到了电极压力和电阻热的影响，使板材发生局部变形和组织改变。热影响区内的塑性环(Corona bond, CB)是在电阻点焊过程中形成的具有一定塑性的环形区域。塑性环在宏观上形成了板材间的界面间隙，如图6c和图6b所示。从微观上，塑性环中晶粒的尺寸介于母材和熔核内部之间，经历的最高温度高于固相线低于液相线。沿晶界分布的低熔点共晶相或杂质相发生部分液化，使板间熔核结合面形成粘接。缩孔位于熔核区中心，其周围有微裂纹。缩孔的位置也随着熔核区向下层板偏移，即缩孔处于NCS区下方。熔核边部几乎没有或只有少量的缩孔，因为在凝固过程中熔核边缘最先冷却凝固，且熔融态金属在快速冷却凝固过程中发生的体积收缩较大，使内部形成收缩孔洞，进而形成缩孔。由于焊接过程中温度梯度较大，加热及冷却极快，使接头中产生飞溅，如图7所示。对用超声波检测仪筛选出有飞溅缺陷的接头进行破坏性检查，发现其内部都有较大的缩孔。其原因是，焊接时熔核区内部的液态金属突破了热影响区的束缚喷射到熔核区外，时熔核区内的液态金属减少而形成了缩孔。实验结果表明，不锈钢点焊接头中的主要缺陷，是飞溅(其中有缩孔)、缩孔和微裂纹。
图7
图7
电阻点焊接头中的飞溅和缩孔缺陷
Fig.7
Splash and shrinkage defects in resistance spot welding joints
图8
图8
显微硬度和强度实验装置和测量结果
Fig.8
Hardness and strength testing device and mea-surement results(a) hardness measurement results(b) location strength measurement results
2.2 接头的硬度和强度
不锈钢电阻点焊接头的显微硬度如图8a所示。可以看出，熔核与母材的显微硬度分别约为210HV1和225HV1。热影响区的硬度比熔核和母材的约低190HV1。其原因是，在焊接过程中该区域受到电阻热和电极压力的影响，其最高温度高于固相线而低于液相线而部分熔化，晶粒比熔核内的粗大，从而使其硬度偏低，即局部软化。
为了验证显微硬度试验结果的可靠性和准确性，对接头进行了IBIS微区性能表征。拟合后，不同区域的力-深度曲线如图8b所示。可以看出，母材区、熔核区和热影响区相同压痕深度所需的加载力依次减小。三个区域的压痕深度为135 μm，所需的加载力分别为427 N、467 N和550 N。使用IBIS力学性能仪器计算出热影响区的抗拉强度为560 MPa，比母材的强度740 MPa和熔核的强度650 MPa分别降低了180 MPa和90 MPa。这表明，在这三个区域中热影响区的强度值最低，硬度的测试结果一致。
2.3 接头的力学性能
对不同厚度组合的双层板接头进行拉剪实验，以找出影响接头力学性能的关键因素。同时，硬度分析和微区力学性能表征的结果表明，热影响区内的塑性环是接头区域中强度最低的，表明热影响区出现了局部软化，可能是接头拉剪失效的关键因素。因此，结合拉剪实验中接头的断裂形式和断口分析，可进一步明确在拉剪过程中接头的失效机理。
同时，用超声波检测仪器对不同厚度组合的双层板接头(如0.8 mm + 1 mm、1.5 mm + 2 mm和3 mm + 4 mm)进行超声波螺旋C扫描成像检测，并筛选不同熔核直径的点焊接头进行拉剪实验，以研究接头力学性能与熔核直径的关系。根据试验结果，接头的熔核直径与最大载荷之间的关系，如图9所示。
图9
从图9可见，接头的力学性能与熔核直径有高度的相关性。随着熔核直径的增大最大拉剪力随之增大，其Pearson相关系数为
式中
由薄板组成的双层板接头，单位熔核直径增大使最大拉剪力增量减小；但是在厚板组成的双层板接头中，单位熔核直径增大使最大拉剪力增量增大。这表明，随着双层板接头厚度的增加，单位熔核直径增量导致的最大拉剪力增量随之增大，即如图9中拟合曲线斜率的变化。
2.4 接头的宏观断口形貌
穿核断裂形式的宏观断口形貌如图10a所示，各区域的断口形貌分别如图10b~f所示。从图10a可见，熔核的宏观形貌呈椭圆形。图10b给出了热影响区中塑性环的断口形貌，可见塑性环受到电加热的影响在板间出现了弱结合区。弱结合区的硬度和强度都比较低，在拉剪过程中塑性变形较小，能承载的力也最小，断口几乎没有韧窝。从图10c可见，熔核边缘断口表面分布着大小不等的韧窝，表明该区域具有韧性与脆性混合的断裂特征。宏观上可观察到的撕裂楞，可能与枝晶方向有关，枝晶界面强度较低则易于开裂，属于放射区。图10d给出了熔核心部区域的断口形貌，表明该区域为等轴晶区开裂，整个断面表现出典型的韧性断裂特征，撕裂棱的边缘有大量韧窝，分布均匀且大小相近，韧窝较大且较深，属于纤维区。图10e、f给出了熔核内缩孔的断口形貌。缩孔是熔核凝固时补缩不足以及熔核内外存在温度梯度所致，在拉剪过程中未受力也未出现韧窝。
图10
图10
电阻点焊接头穿核断裂的显微组织
Fig.10
Microstructure of the resistance spot welded joint spot inner fracture(a) fracture (b) b of fracture (c) c of fracture (d) d of fracture (e) e of fracture (f) f of fracture
图11
图11
电阻点焊接头沿核断裂的显微组织
Fig.11
Microstructure of the resistance spot welded joint spot outer fracture(a) fracture (b) morphology of fracture
因此，对比两种类型的断口形式和形貌，可见热影响区中塑性环的断口表面由微量的焊接组织。焊接热量不足使塑性环部位类似于“虚焊”，承载的拉剪力较小、容易萌生裂纹，成为拉剪断裂的起始区域。
拉伸剪切实验结果表明：熔核直径偏大时接头往往出现沿核断裂，反之将出现穿核断裂，其根本原因是点焊接头在拉剪载荷下受力状态间存在竞争。点焊接头在拉剪载荷下(Fs)熔核内部主要受剪应力(Fb)，而熔核周围受拉应力(Fa)，如图12所示。剪应力与拉应力竞争且都有一个临界值，驱动力达到临界值后接头断裂，熔核直径是临界值的关键因素之一。较大的熔核直径使熔核能承受的剪应力大于拉应力，使接头发生沿核断裂。反之，发生穿核断裂。
图12
3 结论
(1) SUS301L不锈钢的电阻点焊接头由母材区、熔核区和热影响区三个典型区域组成。在熔核边部呈现出沿凝固过程中热流方向排列的柱状枝晶组织，而熔核心部则为等轴枝晶组织。在热影响区内，沿晶界分布的低熔点共晶相或杂质相部分液化，使板间结合面粘接而形成塑性环。
(2) 接头的主要缺陷有飞溅、缩孔和微裂纹，飞溅伴随着出现缩孔。受凝固速度的影响，在熔核的心部区域出现缩孔。接头的母材区、熔核区和热影响区的硬度和强度依次降低。热影响区中局部软化部位的塑性环，是拉剪开裂的起始区域。
(3) 接头的强度与熔核直径高度正相关。随着双层板接头厚度的增加，单位熔核直径的增量产生更大的最大拉剪力增量。拉剪的失效模式，分为穿核断裂和沿核断裂，熔核的直径影响接头的断裂形式。
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[J].
TRIP (transformation induced plasticity) 980 high strength steel and SPCC (steel plate cold common) low carbon steel of about 1.5 mm in thickness were welded by resistance spot welding. The optimal welding parameters were acquired according to the test results of the joint shear tensile load. Then the performance and microstructure of the spot welded joint prepared by the optimal process were characterized by means of electronic tensile testing machine, micro-hardness meter, OM, SEM, EBSD and EDS. Results showed that the metallurgical bonding between the two base materials is realized, the molten nuclear of the spot welded joint is oval and has large deviation, molten nuclear of the side of SPCC steel is smaller than that of the TRIP980 one. The interface can obviously be observed in molten core region of spot welded joint. Shear tensile fracture of the spot welded joint is located at the interface, which is close to the edge of fusion zone of the side of SPCC steel, and the fracture is brittle fracture. The microhardness of molten nuclear on the side of the SPCC steel is lower than that of the TRIP980 one, but there existed a peak value of the hardness of nugget zone on the side of the SPCC steel. Elements of C, Mn, Si and Al etc. presented different diffusivity in the molten nuclear, and of which the concentration declines from the side of the TRIP980 steel to that of the SPCC one. The microstructure of the side melting zone of SPCC low carbon steel is quite different. The microstructure near the parent material is soft ferrite. The microstructure near the nugget side is hard martensite. The stress concentration caused by this difference is the main reason that affects the mechanical properties of the joints.
TRIP980高强钢/SPCC低碳钢的异种钢板电阻点焊接头组织及力学性能研究
[J].采用电阻点焊对1.5 mm等厚TRIP980高强钢/SPCC低碳钢板进行焊接。以点焊接头的拉剪载荷为评价指标。 利用电子拉伸试验机、显微硬度仪、OM、SEM、EBSD、EDS对所获得的较优焊接参数时的点焊接头性能及显微组织进行测试和分析。结果表明,点焊接头的熔核呈椭圆形,熔核由SPCC低碳钢侧向TRIP980高强钢侧偏移;点焊接头的拉剪断裂位置发生在结合面边缘近SPCC低碳钢侧的熔合区处,断口为脆性断裂;SPCC低碳钢侧熔核硬度低于TRIP980高强钢侧,但SPCC低碳钢侧熔合区硬度出现峰值;母材的部分互熔使熔核中C、Mn、Si、Al等元素浓度由TRIP980高强钢侧到SPCC低碳钢侧均匀递减;近SPCC低碳钢侧熔合区组织差异较大,近母材侧为软相铁素体,近熔核侧为硬相马氏体,这种组织差异导致的应力集中是影响接头力学性能的主要原因。
Dissimilar high- strength steels: fusion welded joints, mismatches, and challenges
[J].
Defect intelligent identification in resistance spot welding ultrasonic detection based on wavelet packet and neural network
[J].
Study on cracking and fatigue property of stainless steel resistance spot welding under different conditions
[J].
运行条件对不锈钢点焊疲劳性能影响及开裂分析
[J].
Overall residual stresses in the resistance spot welding joint of dissimilar aluminum alloys
[J].
异种铝合金电阻点焊接头全场残余应力研究
[J].基于仪器化压入试验和有限元理论，建立考虑接头微区力学性能的热-电-力耦合的异种铝合金电阻点焊有限元模型，并用该模型模拟5083与7N01铝合金电阻点焊接头截面上的整体残余应力场分布。用金相显微镜、硬度测试仪和全释放应变法获得点焊接头的熔核形貌、硬度分布及上下表面的残余应力，探讨点焊前后微区力学性能变化对接头残余应力大小及分布的影响。试验结果表明，5083与7N01铝合金进行电阻点焊后，熔核和热影响区材料发生软化，其硬度和流动应力与7N01母材相比明显降低。模拟结果表明，接头微区力学性能变化对残余应力分布规律的影响较小，对残余应力的峰值影响较大，熔核处于三向拉应力状态且熔核心部的残余应力最大。考虑微区力学性能的有限元模型计算得到的残余应力与试验测试结果一致，证明模型的有效性。
Optimization of resistance spot welding quality prediction based on improved sparrow search algorithm for BPNN
[J].
基于改进麻雀搜索算法优化BPNN的电阻点焊质量预测
[J].
Influence of adhesive sealant on resistance spot welding of stainless steel sheets with different thickness
[J].The influences of adhesive sealant on weldability, nugget morphology, mechanical property and manufacturing process of resistance spot welding were systematically studied by 301L stainless steel with obvious different thickness (close to 7∶1) of sheets. The results show that the thermal decomposition processes of adhesive sealant may change current density distribution, which in turn affects the nugget diameter and penetration depth, and finally change the acceptable current range. In addition, the introduction of adhesive sealant has little effect on the weld spacing, and also shows a good tolerance to the initial gap.
密封胶对差厚不锈钢板电阻点焊接头的影响
[J].以板厚差异明显（板厚比接近7∶1）的301L不锈钢板组合为研究对象，系统研究了密封胶对电阻点焊可焊性、熔核形貌、力学性能和生产因素的影响规律。研究结果表明，密封胶受热分解过程可以改变电流密度分布，进而影响熔核直径和熔透深度，使得可接受电流范围发生变化。此外，密封胶的引入对焊点间距设计基本无影响，对板材间隙尺寸也表现出较好的容忍度。
Effects of electrode morphology on microstructures and mechanical properties of spot welded Al-steel joints
[J].
电极形状对铝-钢点焊接头组织及力学性能的影响
[J].研究6061-T6铝合金-SUS301L不锈钢异种金属电阻点焊接头的微观组织特点及电极形状的影响规律。结果表明，铝-钢点焊接头具有熔-钎焊特征，铝合金熔核由α-Al胞状晶、胞状树枝晶和树枝晶组成，铝/钢界面层具有双层结构，靠近铝熔核侧主要为细针状Fe<sub>4</sub>Al<sub>13</sub>，靠近不锈钢侧主要为Fe<sub>2</sub>Al<sub>5</sub>金属间化合物，接头主要为界面断裂模式，铝/钢界面是点焊接头最薄弱的区域。电极形状对铝合金-不锈钢点焊接头具有明显的影响。获得的优化电极形状为：不锈钢侧为圆形平面电极，电极端面直径为10 mm;铝合金侧为球面电极，球面半径为35 mm。在优化电极条件下，铝合金-不锈钢点焊接头的熔核直径、拉剪力及压痕率分别为7.5 mm、4.7 kN和13.5%。与采用F型电极相比，其熔核直径和拉剪力分别提高53.1%和56.7%，压痕率降低47.3%。因此，采用优化电极更有利于改善铝合金-不锈钢电阻点焊接头的力学性能及表面质量。
Microstructure and mechanical properties of AZ31B magnesium alloy / 304 stainless steel resistance spot weld joint with high entropy alloy powder
[J].
添加高熵合金粉末AZ31B镁合金/304不锈钢电阻点焊接头组织和力学性能
[J].以FeCoNiCrMn高熵合金为中间层，获得高质量的AZ31B/不锈钢电阻点焊接头。分析过渡区与两侧母材的反应扩散行为，检测接头性能并优化焊接工艺。结果表明：包含FeCoNiCrMn颗粒的过渡区成功连接镁、钢两母材。镁合金侧界面主要是颗粒周围反应生成的Fe<sub>4</sub>Al<sub>13</sub>金属间化合物；而不锈钢侧边界主要由（Fe，Ni）固溶体和Fe<sub>4</sub>Al<sub>13</sub>金属间化合物两部分组成。拉剪载荷F随焊接电流I和焊接压力P的增加，焊接时间t的延长，呈现出先升高后降低的趋势，在18.2~22.5 kA，15~35周波，2.0~10.6 kN的实验工艺范围内，添加高熵合金镁/钢点焊接头拉剪载荷在3.2 kN以上，最大拉剪载荷为5.605 kN，相比未添加高熵合金镁/钢点焊接头拉剪载荷提高了397%。高熵合金过渡层形成了大量（Fe，Ni）固溶体，减少Fe<sub>4</sub>Al<sub>13</sub>脆性金属间化合物的生成，有效提高了接头的力学性能。
Statistical modeling and optimization of resistance spot welding process parameters using neural networks and multi-objective genetic algorithm
[J].
Ultrasonic non-destructive testing and evaluation of stainless-steel resistance spot welding based on spiral C-scan technique
[J].
Synthetic aperture imaging technology for ultrasonic spiral scanning detection of metal bars
[J].Spiral scanning mode, where ultrasonic probes relatively rotate forward around a tested bar, is commonly used in an automatic ultrasonic testing system for metal bar quality control. Current nondestructive testing standards for bars with ultrasonic technology specify that whether the bar is rejected or accepted should be made in accordance with the amplitude of the echo from a defect in the bar. The quality information obtained by the abovementioned standard testing procedure is only the echo from the defect, and it is too simple to characterize the defect in detail and accurately. Therefore, inspection using imagery and quantitative nondestructive testing (QNDT) of bar quality is the development trend of bar quality control technology in the future. In achieving QNDT of metal round bars, a synthetic aperture focusing on imaging algorithm in a polar coordinate system (pSAFT) and its surrounding scan-mode time-domain synthetic aperture focusing technology (ST-SAFT) were proposed in accordance with the classical ultrasonic synthetic aperture focusing technology (SAFT) theory on a Cartesian coordinate system. Based on the signal set collected by the spiral scanning automatic detection system, the formula of time-delay superposition imaging expressed by the effective synthetic aperture radian was deduced to image the defects in the bar with a cross-sectional view. By preparing a transverse-hole artificial defect sample for the testing experiment, ultrasonic testing data were processed by ST-SAFT, and then a circular section tomography was imaged. Image edge recognition was used to quantitatively evaluate the sizing ability and positioning resolution of ST-SAFT for defect detection. Experimental results show that the measured value of artificial defects with ST-SAFT is equivalent to the real value; the positioning of the transverse side-drilled hole is accurate, and the imaging resolution is significantly better than that of B-scan. The imaging speed for each circular section can reach the order of milliseconds, which can match the mechanical scanning speed of bar inspection for one circle. Therefore, this technology can be used to improve the technical level of ultrasonic automatic testing equipment for metal round bars and ensure safety of the application of metal round bars.
金属圆棒超声螺旋扫査检测的合成孔径成像技术
[J].为实现金属圆棒的定量无损检测(QNDT)，在经典的Cartesian坐标系超声合成孔径(SAFT)理论指导下，提出了极坐标系下的合成孔径聚焦成像(pSAFT)算法及其环绕式时域合成孔径聚焦技术(ST-SAFT)。基于螺旋扫查自动检测系统推导了采用有效合成孔径弧度(SAR)表示的延时叠加成像表达式；通过制备横孔型人工缺陷试样进行检测实验，将超声检测数据经ST-SAFT处理后成像为圆截面断层扫描图；再运用图像边缘识别法进行定量评价该方法对缺陷检测的定量定位分辨率。结果表明：ST-SAFT孔径测量值与实际值相当；横孔定位准确；成像分辨率显著优于B扫描结果；每圆截面成像速率可达毫秒量级，可与棒材检测一周的机械扫查速率相匹配。该技术可用于提升金属圆棒超声检测设备的技术水平和提高棒材使用安全性保障能力。
Fea of evaluation material yield strength and strain hardening exponent using a spherical indentation
[J].
球形压痕法评价材料屈服强度和应变硬化指数的有限元分析
[J].
Study on fatigue behavior and fracture mechanism of aluminum/steel spot welded joints
[J].
铝/钢点焊接头的疲劳行为及断裂机理研究
[J].
Effect of long-term aging on properties of low expansion superalloy GH2909
[J].The microstructure and mechanical properties of a new type of low expansion superalloy GH2909 after long time exposure up to 2000 h at 550℃, 600℃ and 650℃ respectively were investigated. The results show that the alloy had a good microstructure stability and high mechanical properties, namely a slightly increase in strength and little change in plasticity, after aging at 550℃ and 600℃ for 2000 h. However, after 2000 h aging at 650℃ the mechanical properties of the alloy dropped significantly: the strength at room temperature and high temperature decreased significantly, and the plasticity decreased at room temperature, especially the reduction of area at room temperature decreased sharply, but the plasticity increased significantly at high temperature. This is mainly due to the precipitation of a large number of needle-like ε/ε″ phases that penetrate the grains and have "Widmanstatten structure"-like morphology in the microstructure of the alloy during the long-term aging process at 650℃, resulting in a significant reduction in the quantity of strengthening phase γ′ phases. At the same time, the stability of γ′ phase decreases at 650℃ and the size of γ′ phase increases significantly.
长期时效对低膨胀高温合金GH2909性能的影响
[J].
