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SnAgCu-xTi在单晶硅表面的润湿行为

隋然, 林巧力

隋然, 林巧力. SnAgCu-xTi在单晶硅表面的润湿行为[J]. 焊接学报, 2020, 41(4): 90-96. DOI: 10.12073/j.hjxb.20191122001
引用本文: 隋然, 林巧力. SnAgCu-xTi在单晶硅表面的润湿行为[J]. 焊接学报, 2020, 41(4): 90-96. DOI: 10.12073/j.hjxb.20191122001
SUI Ran, LIN Qiaoli. Wetting behavior of monocrystalline Si by SnAgCu-xTi alloys[J]. TRANSACTIONS OF THE CHINA WELDING INSTITUTION, 2020, 41(4): 90-96. DOI: 10.12073/j.hjxb.20191122001
Citation: SUI Ran, LIN Qiaoli. Wetting behavior of monocrystalline Si by SnAgCu-xTi alloys[J]. TRANSACTIONS OF THE CHINA WELDING INSTITUTION, 2020, 41(4): 90-96. DOI: 10.12073/j.hjxb.20191122001

SnAgCu-xTi在单晶硅表面的润湿行为

基金项目: 国家自然科学基金资助项目(51665031);兰州工业学院青年科技创新项目(19K-019);兰州工业学院开物创新团队项目(18KW-05).
详细信息
    作者简介:

    隋然,1983年出生,硕士,讲师;主要从事异种金属连接方面的科研和教学工作;发表论文20余篇;Email:dandansuiran@163.com

    通讯作者:

    林巧力,教授;Email:lqllinqiaoli@163.com.

  • 中图分类号: TG 454

Wetting behavior of monocrystalline Si by SnAgCu-xTi alloys

  • 摘要: 采用改良座滴法在高真空条件下研究了熔融Sn0.3Ag0.7Cu(SAC)-xTi(x为质量分数,%)在800 ~ 900 ℃与单晶硅表面的润湿行为. 结果表明,SAC-xTi/Si体系属于惰性润湿体系,钛的添加显著改善了润湿性. 在不添加钛时,SAC钎料在800 ℃与单晶硅润湿1 800 s后达到平衡,平衡接触角为63°;SAC-1Ti钎料在900 ℃润湿1 800 s后获得最小平衡接触角41°;SAC-3Ti钎料在900 ℃时达到平衡润湿的时间最短,仅为50 s,平衡接触角为48°. 润湿机制为钛加速了单晶硅表面氧化膜的去除. 在熔融钎料的铺展过程中,通过溶解−再析出机制和微掩膜机制,在固/液界面处形成了温度依赖的“金字塔”结构,温度越高,“金字塔”结构越稀疏且形貌越大. “金字塔”结构的出现并未改善体系的润湿性,由于其对三相线的钉扎作用,进而使得体系的润湿性变差.
    Abstract: The wetting behavior of molten Sn0.3Ag0.7Cu (SAC)-xTi (x=wt.%) on the surface of monocrystalline Si at 800−900 ℃ was studied under high vacuum by the modified drop method. The results show that SAC-xTi/Si system belongs to the inert wetting system, and the Ti addition improved wettability, significantly. Without Ti addition, the system achieved the equilibrium contact angle of 63° after 1 800 s at 800 °C; With 1% Ti addition, the system achieved the lowest equilibrium contact angle of 41° after 1 800 s at 900 °C; With 3% Ti addition, the system achieved the fastest spreading in 50 s at 900 °C. The wetting mechanism is that the active component Ti accelerates the removal of oxide film on the surface of monocrystalline Si. During the spreading process of the molten solder, the temperature-dependent “pyramid” microstructure was formed at the solid/liquid interface through dissolution-reprecipitation mechanism and micro-mask mechanism, i.e., the higher temperature induced the sparse and larger “pyramid” microstructures. The appearance of “pyramid” microstructures did not improve the wettability of the system, on the contrary, the wettability became worse due to the pinning of the triple line.
  • 搅拌摩擦焊(friction stir welding, FSW)作为一种固相焊接技术,具有焊缝质量高、变形小等优点[1-2]. 目前加工制造业对焊接智能化、高效化的要求日益上升,机器人搅拌摩擦焊得以更普遍的应用.在实际大型结构的FSW生产中,由于接头形式、板材加工精度以及工装夹具装配质量问题,焊接过程容易产生较大的间隙,对接头的成形和性能极为不利[3-4],当工件之间的间隙超过工件厚度的10%时,很难获得无缺陷质量良好的接头[5]. 间隙的存在导致焊核区(weld nugget zone,WNZ)材料流动不充分,焊缝出现孔洞和隧道等缺陷[6]. 同时,工件被塑化的材料流入间隙,弥补材料缺失使得焊缝位置减薄严重,降低接头承载能力[7].

    研究人员[8-9]采用粉末、焊丝或者补偿条作为填充材料对大间隙下的工件进行FSW,得到成形良好无缺陷的接头,接头与常规FSW接头力学性能吻合,然而,当焊接速度过快时,这些填充材料很容易飞出间隙,从而形成缺陷. 同时填充材料需要在焊前放置在间隙内,针对复杂结构间隙及焊接过程中产生的间隙,填充材料的尺寸以及填料的连续性受到限制.

    基于传统搅拌摩擦焊方法,填充材料旁轴送料,将FSW与填料过程同时进行,实现大间隙机器人搅拌摩擦填丝焊,并对其接头进行盐雾腐蚀试验,分析搅拌摩擦填丝焊接头不同区域的腐蚀行为差异.搅拌摩擦填丝焊提高了FSW对工况条件的适应性,适用于高铁、船舶和飞机上大型及复杂结构焊缝,有望为工程实际应用提供理论依据和技术支撑.

    试验材料为5A06铝合金轧制板材,尺寸为300 mm × 70 mm × 3 mm,填充材料为直径1.6 mm的5B06丝材. 机器人搅拌摩擦填丝焊焊接过程示意图及焊具尺寸如图1所示,对接板材焊接间隙为2 mm. 填充丝材经过高推力送丝系统从送丝孔连续输送到储料腔内部,高速旋转的螺杆将金属丝材剪切成粒状材料,粒状材料在自身重力及与螺杆侧壁的摩擦力的影响下,在储料腔内塑化从底部的缝隙流出. 轴向压力使储料腔与板材之间产生挤压效果,粒状材料发生变形堆积并被塑化. 在旋转的搅拌针的驱动作用下,塑化的填充材料发生流动并实现与基材的连接. 试验所采用的焊接工艺参数为转速3 000 r/min,焊接速度200 mm/min,送丝速度1.8 m/min,轴向压力5 000 N,倾角1.5°.

    图  1  焊接过程示意图及焊具结构
    Figure  1.  Welding process and the welding tool structure. (a) schematic illustration of wire-feeding friction stir welding; (b) dimensions of the welding tool

    图2为机器人搅拌摩擦填丝焊接头焊缝表面形貌. 焊缝表面光滑成形良好,无沟槽缺陷,在搅拌针的驱动作用下,塑化的填充材料发生流动后沉积弥补了间隙位置材料缺失,同时焊缝有一定程度的增厚,提高了接头的承载能力.

    图  2  焊缝表面形貌
    Figure  2.  Surface morphologies of the welds

    图3为焊缝整体微观形貌及不同区域的微观组织. 焊接接头填充材料与基体母材结合良好,焊缝无孔洞及隧道缺陷,由于搅拌针的存在,搅拌针促进塑化的丝材和基材发生流动,提高了填充材料与基材的结合效果. 丝材经过螺杆的剪切及静轴肩的挤压作用,与焊核区受到搅拌针的搅拌作用一样,填充材料也经历了大塑性变形,发生动态再结晶,形成细小的等轴晶.

    图  3  搅拌摩擦填丝焊接头微观组织
    Figure  3.  Microstructures of wire-feeding friction stir welding. (a) microstructures of the cross-section; (b) top interface; (c) thermo-mechanically affected zone interface; (d) filler materials zone

    搅拌摩擦填丝焊接头经过7天盐雾腐蚀试验后接头各区域腐蚀形貌如图4所示. 接头表面均发生了点蚀坑的萌生, 表面出现腐蚀产物;焊核区及填充材料区域的点蚀坑尺寸较小,且分布较为均匀;母材点蚀坑分布不均匀,尺寸较大.热力影响区(thermo- mechanically affected zone,TMAZ)的点蚀坑随晶粒分布特征呈流线分布,热影响区(heat-affected zone,HAZ)的点蚀坑尺寸较大,且出现一定的聚集现象,点蚀坑发生扩展.焊核区和填充材料区表现出更好的耐腐蚀性能.

    图  4  不同区域盐雾腐蚀形貌
    Figure  4.  Salt spray corrosion morphologies in different zones. (a) WNZ; (b) filler materials zone; (c)TMAZ; (d) HAZ; (e)BM

    第二相分布及尺寸对点蚀坑的形成有巨大影响,第二相和基体之间形成微电偶会导致腐蚀现象发生.焊核区经过塑性变形后第二相颗粒被打碎,尺寸较小分布也更均匀,进而发生腐蚀现象后点蚀坑分布均匀细小;填充材料区域拥有更小且弥散分布的第二相颗粒,填充材料的加入增强了焊核区的耐蚀性.经过轧制后的母材中第二相颗粒尺寸较大且分布不均匀,耐蚀性较差易形成较大的点蚀坑;热力影响区点蚀坑呈流线分布,而热影响区第二相颗粒发生聚集长大,发生点蚀后有利于点蚀坑的扩展,导致热影响区的耐蚀性较差.

    图5为热影响区点蚀坑SEM图及附近元素分布.发现在第二相Al6(FeMn)附近产生了明显的腐蚀现象, 点蚀坑发生扩展. 在盐雾环境中,铝合金表面虽然存在一层氧化膜,但是随着溶液中Cl的侵入,Cl破坏了表面氧化膜,促进点蚀现象发生. 同时热影响区第二相颗粒Al6(FeMn)与铝基体之间存在腐蚀电位差形成原电池,由于Al6(FeMn)电位高于铝基体[10],第二相颗粒在腐蚀过程中充当阴极,促使周围基体发生腐蚀,因此在第二相附近形成环形腐蚀区域产生腐蚀坑并向四周扩展. 当第二相尺寸较大时,周围基体溶解的范围增大,点蚀坑的尺寸也会更大. 基于元素分布图可以看出,在腐蚀坑附近Al元素含量减少,点蚀坑内金属发生溶解,点蚀孔内阳离子浓度升高,Cl就会不断侵入以维持平衡.随着Cl浓度的升高发生水解,导致点蚀坑内部氢离子浓度升高,溶液酸化,促使基体进一步溶解,点蚀坑发生扩展.

    图  5  热影响区腐蚀产物及元素分布
    Figure  5.  Corrosion products and element distribution of HAZ

    图6为经过7天盐雾腐蚀接头、未腐蚀接头及母材的拉伸测试结果.未腐蚀接头抗拉强度为388.9 MPa ± 1.4 MPa,断后伸长率为20.5% ± 0.4%,分别达到母材的99%及94%. 经过7天盐雾腐蚀后接头抗拉强度降低到356.6 MPa ± 1.2 MPa,断后伸长率为18.1% ± 0.9%,盐雾腐蚀后接头强度降低了8.3%,断后伸长率下降了11.7%,盐雾腐蚀试验后接头仍保持较优的力学性能. 盐雾腐蚀环境造成焊缝表面出现点蚀坑,而富Cl环境使基体金属进一步溶解,点蚀坑发生扩展,减少了接头有效承载面积,在承受载荷时其易成为薄弱位置,裂纹在点蚀坑位置产生,降低了接头承载能力.

    图  6  焊接接头抗拉强度及断后伸长率
    Figure  6.  Ultimate tensile strength and elongation of joints

    (1) 实现了大尺寸间隙下机器人搅拌摩擦填丝焊,焊接过程与填料过程同时进行,提高了搅拌摩擦焊对接头间隙的容忍性,消除了焊缝减薄问题.

    (2) 填充材料与基材实现了良好的冶金连接,经过剧烈塑性变形后,焊核区和填充材料发生动态再结晶,表现为细小的等轴晶粒.

    (3) 未腐蚀接头抗拉强度达到388.9 MPa ± 1.4 MPa,断后伸长率为20.5% ± 0.4%,分别达到母材的99%及94%. 在腐蚀过程中焊核区和填充材料区耐腐蚀性能优于热影响区与母材,点蚀坑细小且均匀分布,7天盐雾腐蚀后接头保持优异的耐蚀性能.

  • 图  1   SAC-xTi在硅基板表面上接触角及归一化半径随时间的变化

    Figure  1.   Variations of contact angle and normalized contact radius with time for SAC-xTi/Si. (a) contact angle;(b) normalized contact radius

    图  2   SAC-xTi/Si等温润湿后横截面宏观形貌

    Figure  2.   Cross-sectional structures of SAC-xTi/Si system after wetting. (a) SAC-3Ti/Si system after isothermal wetting at 800 ℃;(b) SAC-3Ti/Si system after isothermal wetting at 850 ℃;(c) SAC-3Ti/Si system after isothermal wetting at 900 ℃;(d) SAC-1Ti/Si system after isothermal wetting at 900 ℃;(e) detailed view for e position in Fig. 2d;(f) detailed view for f position in Fig. 2d

    图  3   SAC-3Ti/Si在900 ℃等温润湿后界面微观结构

    Figure  3.   Interfacial microstructures for SAC-3Ti/Si system after isothermal wetting at 900 ℃. (a) vicinity of triple line (cross-sectional view); (b) inner of interface (cross-sectional view);(c) detailed view for c position in Fig. 3b;(d) vicinity of triple line (top view);(e) inner of interface (top view);(f) detailed view for f position in Fig. 3e

    图  4   去除凝固金属后界面处的XRD

    Figure  4.   XRD pattern for the solidified metal removed interface

    图  5   等温润湿后单晶硅基板的XPS

    Figure  5.   XPS of monocrystalline Si substrate surface after isothermal wetting

    图  6   等温润湿后去除凝固金属SAC-xTi/Si界面的锥体结构

    Figure  6.   Pyramidal hillocks of the solidified metal removed interface for SAC-xTi/Si system after isothermal wetting.(a) SAC/Si after wetting at 800 ℃;(b) SAC-Ti/Si after wetting at 850 ℃;(c) SAC-3Ti/Si after wetting at 900 ℃

    图  7   1/cosθe与温度的变化关系

    Figure  7.   Relation curve between 1/cosθe and temperature variation

    表  1   图2e图2f中对应位置的EDS化学成分(摩尔分数, %)

    Table  1   Chemical compositions for the corresponding positions in Fig. 2e and Fig. 2f

    能谱标号SiTiCuAgSn
    166.5232.710.330.050.39
    20.7044.000.360.3550.59
    下载: 导出CSV
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  • 收稿日期:  2019-11-21
  • 网络出版日期:  2020-07-26
  • 刊出日期:  2020-07-26

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