【作者】 陈磊；

【导师】 黄永宪；

【作者基本信息】 哈尔滨工业大学 ， 材料工程（专业学位）， 2018， 硕士

【摘要】 搅拌摩擦焊作为固相连接技术,可避免熔焊缺陷,对于铝合金等轻质材料连接有巨大优势。但由于搅拌摩擦焊固有模式,存在接头减薄、焊后匙孔或缺陷修复以及无法支撑的问题。针对这些问题,对3 mm厚7150-T77511高强铝合金采用无减薄搅拌摩擦焊、固相填充修复和自支撑搅拌摩擦焊实现接头的无缺陷高强连接,获得无减薄接头。本文设计了分体式焊具并对其优化,研究了接头成形、微观组织、力学性能及材料流动行为,为7150-T77511高强铝合金的搅拌摩擦焊无缺陷高性能连接提供技术支持。通过内置小轴肩焊具新颖性设计,利用“一次焊接,二次成形”方式实现了无减薄高强度连接。在焊具转速800 rpm,焊接倾角1.5°,焊速100-400mm/min下,无减薄搅拌摩擦焊接头无缺陷,整个接头分为轴肩作用区、焊核区、热机影响区和热影响区。在一定范围内随焊速增加,接头变窄,晶粒细化,接头抗拉强度提高,最大可达491.8 MPa,达到母材强度的85%,断裂方式为脆性-韧性混合断裂模式。接头显微硬度呈“W”型分布,前进侧更高的焊接温度使部分强化相析出,硬度最低值出现在后退侧的热影响区。材料本身特性导致硬度受热影响区域较宽,焊速增加可提高接头整体显微硬度。通过设计可消耗式焊具,在匙孔或缺陷规则化处理后,采用“以强补弱”方式进行固相修复,实现了匙孔或缺陷的修复。对规则孔和填充棒尺寸优化设计,实现了填充接头的准等强修复,最大抗拉强度达到445.9 MPa,为焊缝强度的90.7%。填充修复接头分为填充区、混合区、新焊核区、焊核区、热机影响区和热影响区。原填充棒部分材料留在修复接头中成为填充区,填充棒材料与规则孔周围材料混合形成冶金连接成为混合区,断后填充棒在搅拌摩擦处理过程中充当搅拌针作用并形成新焊核区。随填充棒尺寸接近到略大于规则孔尺寸时,接头抗拉强度增加,混合区的细小等轴晶为两者材料混合并重新形核长大而成,硬度相比新焊核区和焊核区高,热机影响区和热影响区经历二次焊接热循环,软化严重,成为填充修复接头的最弱区域。通过设计带下支撑体搅拌针分体式焊具,以下支撑体实现背部支撑作用,达到无垫板支撑搅拌摩擦焊连接。优化自支撑搅拌摩擦焊分体式焊具形状尺寸,可适应不同板厚无垫板搅拌摩擦焊连接,尺寸的优化设计避免了轴肩外圈作用区的下榻,消除了常规搅拌摩擦焊背部弱连接和未焊透问题。该方法转速工艺区间窄,在550 rpm下一定范围内增加焊速可以减少甚至消除内部孔洞缺陷,在500 mm/min焊速下实现了无缺陷自支撑搅拌摩擦焊连接。受轴肩和下支撑体作用上焊核区和下焊核区由于结构的相似性和良好的散热条件,晶粒大小基本一致,相比焊核区晶粒更细小,各区晶粒形貌与常规搅拌摩擦焊类似。通过采用无减薄搅拌摩擦焊、匙孔或缺陷固相修复和自支撑搅拌摩擦焊,实现了材料的高强无减薄连接,对焊后匙孔进行了准等强修复,并实现了无法支撑时的搅拌摩擦连接。经焊具设计优化和对组织与性能相关性分析,实现性能优化控制,获得无减薄无缺陷高强搅拌摩擦焊接头。更多还原

【Abstract】 Friction stir welding as solid-state connection technologies can avoid the defects caused by fusion welding.It has great advantages for connecting lightweight materials such as aluminum alloys.This paper uses non-weld-thinning friction stir welding,solid-state filling repair and self-supporting friction stir welding to solve problems of weld thinning phenomenon,keyhole and supporting,a separate welding tool was designed and optimized to achieve defect-free and high-strength connection of 3 mm 7150-T77511 aluminum alloy.The joint forming,microstructure,mechanical properties and material flow behavior were studied,providing technical support for the friction stir welding defect-free highperformance connection of 7150-T77511 aluminum alloy.Through new design of shoulder welder with built-in small shaft,the “single pass welding,two forming action” method achieves no-thinning and high-strength joints.At welding rotating speed of 800 rpm,welding inclination angle of 1.5°,and welding speed of 100-400 mm/min,there is no defect in the thinned friction stir welding joints.The entire joint is divided into four zones: shoulder affected zone,welding nugget zone,thermo-mechanically affected zone and heat affected zone.Within a certain range,with the increase of welding speed,joint width become narrow,grain refinement occurs,tensile strength of the joints increases,up to 491.8 MPa,reaching 85% of the strength of the base metal.The fracture mode is a brittleductile fracture mode.The microhardness of the joints shows a "W" distribution,and the higher welding temperature on the advancing side causes the strengthening phases to precipitate,and the lowest microhardness value appears on the heat affected zone of the retreating side.The characteristic of the material itself results in a wide range of microhardness affected area,and the increase of the welding speed can improve the overall microhardness of the joint.By designing the consumable welding tool,after the keyhole or the defect is regularly treated,the solid-phase repair is performed in a way of “making the weak strong” to realize the repair of the keyhole or the defect.The size of the regular holes and filler rods is optimized to achieve equal strength repair of the filled joints with a maximum tensile strength of 445.9 MPa,equal to 90.7% of weld strength.Fill repair joints are divided into six zones: filling zone,mixed zone,new welding nugget zone,welding nugget zone,thermo-mechanically affected zone,and heat affected zone.The original filler rod material remains in the repair joint formed filling zone.The filler rod material was mixed with the material of regular hole and formed mixed zone.After the fracture,the filler rod acted as a stirring pin and forms new welding nugget zone during the friction stir process.With the filler rod size close to slightly larger than the regular pore size,the tensile strength of the joint increases.The hardness of mixed zone is higher than that of new welding nugget zone and welding nugget zone due to the fine equiaxed grains of mixed zone.thermo-mechanically affected zone,and heat affected zone experienced the secondary welding thermal cycle,the softening is severe and become the weakest area of repairing joints.By designing a separate welding tool with a supporting stirring pin,the supporting achieves a back supporting function and achieves a non-cushion platesupporting friction stir welding connection.Self-supporting friction stir welding can adapt to different sheet thickness without back supporting after optimize the self-supporting friction stir welding split type welding equipment shape and size.The optimized design of the size avoids the outer area of the shaft shoulder,eliminates the weak connection and incomplete penetration of the conventional friction stir welding.The method has a narrow range of rotational speed,and increasing the welding speed with a certain rotational speed at 550 rpm can reduce or even eliminate internal hole defects,and realizes non-defect friction stir welding connection at a welding speed of 500 mm/min.Due to the structural similarity and good heat dissipation conditions,the grain size of upper welding nugget zone and lower welding nugget zone affected by the shoulder and the lower support is basically the same,but smaller compared to welding nugget zone,the grain morphology of each zone is similar to conventional friction stir welding.Through the non-weld-thinning friction stir welding,keyhole or defect solidstate filling repair and self-supporting friction stir welding,high-strength and nothinning connection of the material was realized,the keyhole was repaired and nosupport welding was realized.Through the optimal design of the welding equipment and the analysis of the correlation between the organization and performance,the performance optimization control is achieved,and a no-weld-thinning high-strength welding without defect was obtained.更多还原