励磁电流对6061铝合金MIG焊熔敷层组织及性能的影响

Effects of exciting current on microstructure and properties of welding cladding on 6061 aluminum alloy by MIG welding under longitudinal magnetic field

采用纵向磁场作用的MIG焊熔敷技术,调控励磁电流的大小(0,10,20,30 A)在铝合金上制备熔敷层,以提高铝合金焊接熔敷层的力学性能和耐磨性能。采用光学显微镜观察熔敷层的宏观和微观组织形貌,利用维氏显微硬度仪、球盘式摩擦磨损试验机以及万能拉伸试验机对熔敷层的力学性能进行测试分析。结果表明,添加纵向磁场后,熔敷层晶粒有所细化,但细化效果并不明显。在励磁电流为10,20 A时,熔敷层中析出黑色的细小杂晶相,它们在α-Al相中广泛分布,对熔敷层显微硬度、耐磨性和抗拉强度产生影响。当励磁电流为20 A时,熔敷层的硬度比其他励磁电流强度条件下提高了10%~20%,同时熔敷层磨损质量较小,约为1.0 mg,仅是无磁场时磨损质量的一半。此外,熔敷层的抗拉强度随励磁电流增大而提高,在励磁电流为20 A时达到最大值,约为276 MPa。总之,在铝合金MIG焊过程中施加励磁电流能够影响熔敷层组织,提升熔敷层的性能。但是,施加更大的励磁电流会导致电弧热效率升高,使得短时间内大量热量在熔敷层中累积,导致晶粒粗化且材料软化,熔敷层力学性能反而降低。

To improve the mechanical properties and abrasion resistance of welding cladding on 6061 aluminum alloy, a longitudinal magnetic field was introduced to the metal inert gas( MIG) welding. The effects of exciting current on the micro-structure and the mechanical properties of the cladding on the alloy were studied by using optical microscope, Vikers micro-hardness tester, friction and wear testing machine and universal tensile testing machine respectively. Results showed that grain refinement occurred on the welding cladding on 6061 aluminum alloy after introducing the longitudinal magnetic field to the metal inert gas(MIG) welding, especially when the applied excited current were 10 and 20 A. Meanwhile, a certain of new-formed mottle crystal phases was observed in the cladding.Such microstructure benefited the increasing microhardness, tensile strength and the decreasing weight loss after worn of the cladding as exciting current increased from 0 to 20 A. Moreover, the microhardness of welding cladding and substrate increased with excited current and it reached the maximum when the excited current was 20 A at which the microhardness was 10% ~20% bigger than that at other current. For abrasion resistance of the welding cladding,severe worn occurred when there was no longitudinal magnetic field introduced and the wear mass was about 2.1 mg that approximated the value at 30 A. However, from 0 to 20 A, wear mass was found an increase and it was almost the same(1.0 mg) for 10 and 20 A which was only half of that without longitudinal magnetic field. Similarly, tensile strength of the welding cladding increased with increasing the excited current from 0(259 MPa) to 20 A(276 MPa)which was the biggest. However, the tensile strength experienced a reduce at 30 A. Overall, the excited current could definitely influence the structure and properties of the welding cladding on 6061 alloy by the metal inert gas( MIG) welding technique if a longitudinal magnetic field was introduced. However, the applied excited current couldn′ t be too big because the heat efficiency of arc would be quite high, leading to a shear amount of heat accumulation in the cladding. As a result, the mechanical properties and abrasion resistance of the cladding would degrade.