Increasing concern with fuel consumption leads to widespread interest in lightweight structures for transportation vehicles. Several competing technologies are available for the structural connections of these structures, namely welding, mechanical fastening/riveting, and adhesive technologies. Great interest is dedicated to welding of lightweight structures, particularly because of economic reasons derived of part count reduction, faster and cheaper fabrication, and possible weight gains.
However, drawbacks of welding include variation of properties in the welcomed area, intrinsic metallurgical difficulties sibyl leading to unacceptable defects, as well as, from a mechanical design point of view, possibly detrimental fatigue behavior features associated with the continuous path of crack propagation. Crucial factors for the application of new technologies are the cost. Especially for the substitution of metals by light weight alloys beneath all technological properties of the economic aspects have to be considered.
Currently the technological processes receiving more widespread interest in metallic lightweight structures are laser beam welding (LB) and friction stir welding (FSP). According to E. Schubert, M. Classes ET. AL Light weight components are of crucial interest for all branches that produce moving masses. The aim to reduce weight has to be accompanied by high production efficiency and component performance. Laser beam Joining offers the possibility to manufacture Joints of all light metals and their combination. Laser welding is a high energy beam process and in this regard is similar to electron beam.
With that exception they are unlike one another. The energy density of the laser is achieved by the concentration of light waves not electrons. The laser output is not electrical, does not require electrical continuity, is not influenced by magnetism, is not limited to electrically conductive materials and in fact can interact with any material whether it be metal, plastic, wood, ceramic, etc. Finally its function does not require a vacuum nor are x-rays produced. Friction-stir welding (FSP) is a solid-state Joining process (the metal is not melted) that uses a third body tool to Join two facing surfaces.
Heat is generated between the tool and material which leads to a very soft region near the FSP tool. It then eugenically intermixes the two pieces of metal at the place of the Joint, then the softened metal (due to the elevated temperature) can be Joined using mechanical pressure (which is applied by the tool), much like Joining clay, or dough. It is primarily used on aluminum, and most often on extruded aluminum (non-heat treatable alloys), and on structures which need superior weld strength without a post weld heat treatment.
Methodology of the Researches According to the Journal of R. Brushstrokes et al. Joining technology of lightweight dissimilar metals between magnesium and aluminum alloys are essential for legalizing hybrid structure cars and other engineering application. In the present study, the normal center line welding of lap Joint was carried out by laser welding. It was found that the intervocalic layer formed near interface between two metals significantly degraded the Joining metal, which contributes to control thickness of intervocalic compound layer.
Based on the result of FEM. analysis, the edge line welding of lap Joint was carried out, which could easily control the thickness of intervocalic layer and successfully obtained high Joining strength. In comparison with the Journal of R. Brushstrokes et al. According to T. Mortising et al. Macrostructure and mechanical properties of dissimilar welding Joint between AY alloy and MGM alloy by laser welding was very brittle because of building up MGM AAA intervocalic compounds in fusion zone.
On the other hand, FSP is anticipated to welding dissimilar alloys AY alloys and GAZA magnesium alloy with various tool rotational speed
Results and Findings of the Researches In accordance with R. Brushstrokes et al. After tensile-shear tests, it was found that failure occurred inside intervocalic compound layer, which degraded strength of the Joint. The maximum failure load and strength obtained for the welding lap Joint were NON and 20 Amp. This failure load is about 37% of yield load of AY-O alloy. Results of the tensile test of T. Mortising et al. The tensile strength of base was 244 Amp in aluminum alloy and 241 Amp in magnesium alloy. The Joint efficiency was achieved 61% of the strength of the base material. FSP has several disadvantages.
As it is a solid state process, a great amount of tool wear takes place during the plunging stage as the work piece material is cold at this time. Weld speeds in FSP are slower which can lead to time-consuming Joining process. As higher weld forces are required during this process, equipment used for FSP is massive and expensive. Moreover friction stir welding of high melting temperature materials, such as steel and stainless steel are known to have welding tool limitations. Therefore, the use of standard FSP machines runs into high capital cost requirements and relatively poor productivity.
LB has advantages precise working with exact placing of the energy spot, welding of complicated Joint geometry, low heat application, therefore minor changes in macrostructure, low thermal distortion, cavity-free welds, low post weld operation times, large working distance is possible ( welding up to 500 mm distance and also to inaccessible parts). And it’s disadvantages are The welding plants are expensive, depending upon the equipment, If filler material is necessary they are, because of the limited amount produced, relatively expensive.
Analysis and Recommendation of the Researches: It was difficult to obtain enough quality welding strength in welding lap Joint between magnesium and aluminum alloy plates due to intervocalic compound layer formation it was found that the edge-line welding lap Joint could realize the shallow penetration depth of molten metal into lower plate, which would be effective for educing the reaction between two metal and then the formation of intervocalic compound.