Nd

Abstract

As environmental awareness grows among consumers as well as government agencies, attempts to improve fuel economy in automobiles are accelerating. Magnesium and magnesium alloy, as the lightest structural material, are about 40% lighter than aluminum and as much as about 78% lighter than steel.

Besides, magnesium alloys have many advantages such as a low density, high strength/weight ratio, good castability, high damping capacity and well recycle.

Meanwhile, it is required for widening the field of application of magnesium alloys that joining process such as tungsten inert gas welding(TIG), friction stir welding(FSW) and laser beam welding(LBW).

The main problems associated with magnesium alloy welding by conventional processing methods are the inflammability, a tendency toward crack formation and the appearance of porosity during solidification. Laser welding technology is a promising means for overcoming these difficulties.

Laser welding, augmented by the use of shielding gases, provides effective protection of the metal against the action of oxygen and results in a narrow heat affected zone(HAZ). As a consequence, laser beam welding is a prime choice for fusion welding of magnesium alloys.

However, up to now the purpose of main studies for magnesium have been developed of new magnesium alloy and welding of die-casting. Thus, the investigation of wrought magnesium alloy by laser is still limited.

This study is related to the laser weldability of AZ31B magnesium alloy, an all-purpose wrought alloy with good strength and ductility. In the automobiles, the main types of joint are butt and lap. Thus, we investigated the weldability of these joints by 4kW Nd:YAG laser.

The effect of welding parameters on the weldability of butt and lap joints were examined in more detail. Also, the mechanical properties of butt welded joints were investigated by tensile and hardness tests.

On the other hand, because of magnesium is sensitive in oxidation environment, the effects of shields gases and conditions were examined. For this purpose, front and back shield were carried under various shield gases and flow rates.