7×××系空心铝型材挤压横向焊缝的研究

Transverse Welds of 7××× Hollow Aluminium Alloy Profile

目前高速列车的承载结构主要采用7×××系铝合金挤压型材。在铝型材连续挤压生产过程中,2根相邻挤压坯料间的界面会在型材内部形成横向焊缝,而横向焊缝将导致型材性能下降,需要对包含横向焊缝区域的型材进行切除,显著降低了产品的成品率。由于7×××系铝合金硬度较高,材料流动性能较差,所以型材中横向焊缝的延伸长度会大大增加,特别是空心型材中横向焊缝延伸长度增加更为明显,严重影响了产品成品率,因此,开展对7×××系空心铝型材挤压横向焊缝的相关研究具有非常重要的工程意义。回顾了国内外挤压横向焊缝的研究现状,指出了目前该方面研究尚存在的问题,并提出了今后的发展方向。针对7×××系空心铝型材挤压横向焊缝研究中存在的问题,系统研究了空心铝型材横向焊缝的宏观形貌、微观组织等,揭示了挤压工艺参数和模具结构参数对横向焊缝延伸长度的影响规律。结果表明,适当减小挤压比以及增大挤压速度可以有效减小横向焊缝延伸长度,但挤压温度对横向焊缝长度的影响并不明显。

Currently, 7××× aluminum alloy extrusion profiles are widely used in manufacturing bearing structure of high-speed train. During continuous production of aluminum alloy profiles, the interface of two adjacent billets forms transverse weld in the profile. The region including transverse welds must be discarded, so it has great influence on the finished product rate of extrusion production. Due to the high rigidity of 7××× aluminum alloy and low flowing property of material, the length of transverse weld is increased apparently, especially for AA7××× hollow profile, which leads to low finished product rate. Therefore, it is necessary to investigate the evolution of transverse weld for 7××× hollow profile. The current research of transverse weld for hollow profile in literature was reviewed firstly, and the existing problems were pointed out and future development direction was put forward. To solve the problems existing in research of transverse welds of hollow aluminum profiles, the macroscopic morphology and microstructure of the transverse welds of the hollow aluminum profiles were studied in this paper and the influences of extrusion process parameters and die structure parameters on the length of transverse welds were revealed. The reduction of the extrusion ratio and the increase of the extrusion speed can effectively reduce the transverse weld extension length, but the effect of the extrusion temperature on the transverse weld length is not obvious.