Study On Technology Of Laser-arc Hybrid Welding For Ly12 Aluminum Alloy

Owing to low density, high specific strength, high thermal conductivity and goodmachining property, aluminum alloy is widely used in aerospace industry. However, thereare some difficulties in the weld ing of aluminum alloy especia lly high-strength aluminumalloy, limiting their applica tion in more fields . With the advantages of great penetration,high weld ing speed and stable process, Laser-MIG hybrid weld ing has its own merits tosolve the problems in aluminum weld ing. Therefore, in this dissertation, Laser-MIGhybrid weld ing for LY12 aluminum alloy is studied in detail. The ma in results are listed asfollows.The effects of weld ing parameters on laser-MIG hybrid welded LY12 aluminum alloywith different thick ness (2.5mm/5mm) are obtained. It is found that increasing laser powerand arc energy, decreasing weld ing speed can increase bead depth and width. Moreover,for aluminum alloy sheet with 2.5 mm thick ness, increasing weld ing speed will increasethe tendency of bead cracks. In addition, the best weld ing parameters of shield ing gas isobtained by experiment, which is: combined with coaxia l helium gas at flow rate 15 L /min with paraxial 80% helium- 20% argon mixed gas at flow rate 25 L / min.It can be observed that LY12 aluminum alloy sheet with 2.5 mm thick ness issusceptive to hot cracks. The hot cracks are classified into bead center cracks, fusion linecracks, oxide pores cracks and microcracks , in which bead center cracks are the mostcommon. The results show that reducing the arc voltage and weld ing speed can restra in thetendency of cracks. Moreover, using wire ER4043 and filling with titanium powder onLY12 aluminum alloy sheet are also in favor of the avoid ing of cracks.It can be found that the microstructure from the base meta l to bead center is columnardendrite, equia xed dendrite and equia xed dendrite in sequence . After the post-weld heattreatment, the microha rdness of fusion zone is close to that of base meta l. Besides, thetensile strength of LY12 aluminum alloy hybrid welds with 2.5 mm thick ness can reach74.5% of base meta l, while those with 5mm thick ness can reach 80% of base meta l.