Laser Welding Process And Porosity Formation Mechanism Of DP780 Galvanized Steel

Porosity is the main drawback of galvanized steel sheet welding.Due to its high strength,good weldability and high initial work-hardening rate,galvanized duplex steel is widely used in the automobile manufacturing and other industries.The zinc vapor generated during the welding process of the galvanized sheet can easily lead to the porosity defect of the welded joint.In order to investigate the escape process of the zinc vapor produced during laser welding of galvanized high-strength steel plate(DP780),a high speed camera is used to record this escape process and channels.By observing zinc vapor escape process and analyzing the actual formation rate of porosity under the process parameters such as welding power,welding speed and defocus amount,it was summarized the channels of zinc vapor escape and proposed a method for obtaining low porosity,that is,it controls the dynamic balance of the three channels of zinc vapor escape.The experimental results showed that this method can well explain the splashing and external porosity defects of galvanized high strength steel plate,and improved the welding process parameters,so as to improve the efficiency of zinc vapor escape and the welding quality and appearance of galvanized high strength steel plate.In this paper,the DP780 galvanized dual phase steel for 0.8mm and 1.8mm was used for laser lap and surfacing test of 4kW continuous fiber lasers.By adjusting the gap between the two plates,the laser power,welding speed,defocused,it was studied that the influence of process parameters to the forming of welded joints.At the same time,it was studied that the influences of parameter on welding drop,tensile strength and porosity condition.Finally,it was adjusting of welding process parameters that assessed welding joint to enhance quality.In order to further study the formation mechanism of porosity of galvanized high strength steel plate(DP780)during laser welding,it was used the high-speed camera to observe the escape process of zinc vapor during the welding process.In this paper,it was observe the process of welding the process of zinc vapor escape in the high-speed camera,and summed up the escape route of zinc steam principle as well as put forward formation mechanism of porosity,It was verified the formation mechanism of porosity by designing the reserved gap to control the escape test of the zinc vapor.The results of the porosity of the joint and the prediction of the porosity formation mechanism are in more agreement.The internal porosity is due to the fact that the zinc vapor is always moving in the direction of greater solubility in the molten pool,and the formation of the external pores is due to the mechanical imbalance of the zinc vapor in the molten pool.It is also concluded that the dynamic equilibrium of the zinc vapor escape channel can be reduced by reserving the gap.To further verify whether this principle is only suit for 0.8mm galvanized sheet lap effective or not,it was also designing test for 1.8mm galvanized sheet(DP780).The method can explain 0.8mm and 1.8mm galvanized high strength welding splashing and external porosity defects after analyzed the process of zinc vapor escape and the actual formation rate of porosity under the process parameters such as welding power,welding speed and defocus amount.And it is ameliorating the welding process parameters,improving the efficiency of zinc steam escape and the quality and appearance of galvanized high strength steel plate.