Study Of Microstructure And Mechanical Properties Of CO₂Laser Welded Joint On AZ31B Magnesium Alloy

Magnesium alloys have number of advantages, such as low density magnesium alloy, high specific strength, high specific stiffness, excellent thermal conductivity, and recyclability, now magnesium alloys are so widely used in green lightweight construction engineering materials. There are a wide range of applications in automotive, aerospace, electronic communications and other fields for Magnesium alloys, but there are easy to evaporate, welding difficult to control issues such as magnesium alloy, and therefore its connectivity has also been more and more attention. ventional welding method for welding of magnesium alloys is so much.Since the laser welding process for welding magnesium alloy has many advantages, such as fast speed in laser welding of magnesium alloy welding, small heat in input welding, narrow zone in weld and heat affected, small in weld and welding deformation, etc., so the laser welding of magnesium alloys is got attention in the industry. In this paper, We take the 5mm thick AZ31 B magnesium alloy as the research object, the use of CO2 laser welding, research organizations and testing of welded joints characterized by its mechanical properties, magnesium alloys provide excellent experimental data and theoretical applications in production, the main test results as follows:To the effects of different welding process parameters on molding influence of microstructure and properties of welds and joints for the study. the experimental results show that the process parameters for the welding power 1400W-1600 W and welding speed of 400 mm / min-600 mm / min, we can get a good look weld, the weld narrow, no heat affected zone, the weld area is fine equiaxed, and less internal weld defects such as pores and cracks etc.Through the welded joint microstructure was observed that the main defects are pores and thermal cracking in the AZ31 B magnesium alloy laser welding process. The main reason is that the pores generated during welding, weld solidification due to a sharp decline in the solubility of hydrogen evolution led to a large variety of external or internal factors generated by the molten pool was not any time to overflow.EDS analysis showed that the weld zone due to magnesium, zinc low melting point, boiling point is reached first welding process and solidified, continuous melting longer, thus more evaporation, Resulting in the relative content of the base metal after welding seam relatively lower magnesium and zinc, other alloying element content decreased slightly, but lower compared to magnesium, zinc and less, so the relative content was increased;Hardness test show that weld tensile strength and hardness is relatively high when the power 1600 w to cooperate when the welding speed is 600mm/min. Weld hardness average tests show up 58.6HV, bond area average of 57.8HV, the heat affected zone for 58.1HV. the highest of hardness is Weld, followed by the heat affected zone, the lowest is bond area. Tensile tests showed that CO2 laser welding of magnesium alloy AZ31 B occurred in the weld fracture, tensile strength reached 191.96 MPa, 91.57% of the base material, percentage elongation of 1.64%.