【作者】 钟飞；

【导师】 李晓延；

【作者基本信息】 北京工业大学 ， 材料学， 2005， 硕士

【摘要】 本文主要研究钛合金、铝合金激光焊接接头断裂韧性。对1420 铝锂合金,试验按照美国材料试验学会ASTM B 871-01《铝合金产品撕裂试验标准》进行;对BT20 钛合金,试验按照美国材料试验学会ASTM E1820-01《断裂韧性测量标准试验方法》及英国标准草案BS7448-1997 进行。同时参照美国材料试验学会ASTM E1152《确定J-R 曲线的试验方法》对试验结果进行分析。研究了铝锂合金及钛合金激光焊接接头的硬度分布及显微组织。1420 铝锂合金撕裂试验表明,所有试样的启裂能均高于裂纹扩展能。不论启裂能还是裂纹扩展能,基材均高于焊缝及热影响区,基材L-T 方向高于T-L 方向。断口观察发现,基材的断口表面,特别是T-L 方向存在长而深的撕裂凹槽,焊缝及热影响区试样表面主要是沿晶或沿亚晶的脆性断口。由基材的高韧性到焊缝与热影响区的低韧性,是由于发生了断裂模式的转变,发生了由延性断裂向沿晶脆性断裂的转变。BT20 钛合金断裂试验表明,CT 试样均在裂纹延性启裂并缓慢扩展后,发生脆性失稳断裂。母材的断裂韧性明显高于焊接接头,轧制方向对母材断裂韧性的影响不明显。焊接热影响区的断裂韧性介于母材和焊缝金属之间。本研究采用的焊后热处理没有改善焊接接头的断裂韧性,还有进一步恶化的趋势。添加活性剂对焊缝金属的断裂韧性没有明显作用。更多还原

【Abstract】 Main contents of this research are fracture toughness of Al-Li alloy 1420 and Ti alloy BT20 and their laser-welded joints. The tear test of the 1420 was based on the ASTM B 871-01, “Standard test method for tear testing of aluminum alloy products”. The test of BT20 was based on the ASTM E1820-01, “Standard Test Method for Measurement of Fracture Toughness”and British Standard Draft BS7448-1997. At the same time, experiment result is analyzed according to ASTM E1152, “Test method for J-R curve confirmation”. Meanwhile, hardness distribution and microstructure of the alloy and welded joints were investigated. It is indicated from the tear test of the 1420 that energy at crack initiation was higher than that at crack propagation. Moreover, the energy at both crack initiation and propagation of base metal was higher than that of weld metal and heat affected zone. The energy at both crack initiation and propagation of base metal with L-T direction was higher than that with T-L direction. Fractography showed that there was long and deep tearing grooves on the fractography of the base metal, especially with the T-L direction. However, there was inter-granular or inter-subgranular brittle feature mainly on weld metal and heat affected zone. Transition from the higher toughness of the base metal to the lower toughness of the weld metal and heat affected zone is because of the change of fracture model. The fracture model was changed from ductile void coalescence fracture to brittle inter-granular fracture. Fracture test of the BT20 indicates that brittle unstable fracture occurs after ductile crack initiation and slow propagation for all the compact tension (CT) specimens. Fracture toughness of base metal is obviously higher than that of welded joint, and rolling directions have no obvious effect on fracture toughness of base metal. Fracture Toughness of heat-affected zone is between the base metal and weld metal. Postweld heat treatment not only can not improve the fracture toughness of welded joint, but also has the trend of deterioration. Addition of activating agent has no obvious effect on fracture toughness of weld metal.更多还原