Quality assurance measures for laser welding of aluminum alloy
1, aluminum alloy application characteristics Aluminum alloy is widely used in aviation, aerospace, automotive, machinery manufacturing, shipbuilding, chemical industry and other fields because of its light weight, corrosion resistance, low temperature performance and good mechanical properties. With the country in recent years, the pursuit of energy saving economy, the need for aluminum alloy on a step. At present, automobile industry for aluminum alloy are Al Mg (5000 Series), Al Mg Si (6000 Series) and Al mg Zn (7000 Series) three series, car shell multi with corrosion-resistant weldable 5000 series alloy, and beam column strength requirements of the parts of the high with 6000 or 7000 series alloy. The study shows that the aluminum alloy material can reduce the fuel consumption by and reduce the fuel consumption by 37%. The load of the suspension device is reduced by 18% and the vibration strength is reduced by 5%. At the same time, the major automobile factory to increase investment in research and development of aluminum alloy, aluminum alloy welding has become a basic problem had to be solved. 2, the welding characteristics of aluminum alloy At present, TIG welding, MIG welding and other conventional methods are mainly used to weld aluminum alloy. Size can soften fast too late to using conventional methods of welding heat input quantity lead to weld large and penetration depth is shallow, aluminum alloy fast heat conduction, metallurgy high temperature high amounts of dissolved hydrogen spillover hydrogen porosity (dissolved into the molten pool in the hydrogen evolution of pores, known as metallurgical porosity; not completely melt oxidation film of moisture due to thermal decomposition of hydrogen formation of pores, called oxide pores); due to metallurgical weld metal grain coarsening, welded joint strength is reduced to 40%; aluminum alloy with low melting point and heat conduction, the molten metal flow and the formation of weld appearance; heating area, processing materials are easy to deformation and influences the machining accuracy. It is difficult to guarantee the quality of aluminum alloy welding, and the welding speed is difficult to meet the requirement of mass production. With application of laser processing to enhance the level of penetration, the laser welding of aluminum alloy, heat input quantity is small and concentrated heat source, especially after the advent of fiber laser, laser welding aluminum alloy energy density is more centralized, shorter laser wavelength, high reflection can be improved. The forming effect of the welding of aluminum alloy can be improved obviously by means of laser welding, laser -MIG hybrid welding and double laser beam welding. No matter what kind of welding method, the preparation of aluminum alloy is necessary before welding, which has great influence on the welding quality of aluminum alloy. Before the welding of anhydrous alcohol or acetone wipe the surface of the Aluminum Alloy, with the removal of impurities adsorbed on the surface of the water or oil etc.. In order to prevent the workpiece from being oxidized in the air, it is necessary to carry out mechanical polishing or chemical processing and drying for the work piece, so as to complete the welding as soon as possible. In order to speed up the flow of the molten pool in the welding of aluminum alloy, the copper plate can be added on the back of the aluminum alloy to improve the welding seam forming. When welding, using Ar gas protection, isolated from the air, can reduce the generation of air holes. 3, laser welding aluminum alloy optimization of the quality of the specific measures Aluminum alloy laser welding is started when in the presence of a high reflection phenomenon, seriously affect the material absorption of the laser energy, and the shorter the wavelength, the light absorbing material is better. Therefore, optical fiber laser than CO2 laser on aluminum alloy better absorption. The beam pattern of the fiber laser is better than that of the CO2 laser, and the energy density is more concentrated. Once the material begins to absorb light energy, the reflectivity of the liquid metal to the light is obviously decreased. The twin spot laser welding can significantly improve the porosity, mainly because of the use of dual beam welding, two beams of light to form a relatively large keyhole, to improve the stability of the keyhole, for the gas to escape; compared to the serial double beam, using parallel dual beam laser welding, molten pool temperature gradient is smaller, reducing the liquid metal solidification rate, extend the bubbles to escape time, it contributes to the decrease of porosity tendency; parallel dual beam laser welding can improve the stability of the wire feeding, on the stability of welding quality advantage. The laser welding with filler wire, compared to Aluminum Alloy laser welding, molding can be better. Laser filler wire welding can be compatible with the high energy density of the laser welding and filling wire welding Takahashi and connect ability, for a certain gap weld to ensure good molding effect. Through the choice of different filling materials, the base material can be different from the chemical metallurgy, play a certain alloying elements to supplement and strengthen the effectiveness of. Laser clad welding, through the combination of laser and arc, can effectively eliminate the influence of the laser welding plasma. By adjusting the parameters of the optical wire spacing, blowing, welding torch angles, it is possible to acquire beautiful welding seam, and for thick plate without need to groove or simply open a small groove can be a good weld formation. With powerful laser head, the quality of welding can be stabilized. With the further development of laser processing, the function of the laser head is becoming more and more powerful. At present, developed by the Institute of Scansonic HighYAG laser head, can in a certain range of floating around without changing the spot size, does not affect the light wires with, is very conducive to mass production, can improve material processing due to the small size caused by the deviation of weld defects. The welding quality can be guaranteed by the appropriate welding parameters. Fig. 8 optimization parameters of laser power and welding speed of 6061 aluminum alloy laser welding. It can be seen from this figure that the optimal matching parameters of laser power and welding speed are in a straight line, and the slope is basically unchanged. Each given laser power value, in the optimization of the parameters of the curve has a good