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Journal of Materials Processing Technology 218 2015 62 70 Contents lists available at ScienceDirect Journal of Materials Processing Technology jo ur nal home p ag e Mechanical constraint intensity effects on during laser welding of aluminum alloys Xiaojie Wang a Fenggui Lu a Hui Ping Wang b Haichao a Shanghai b a Article Received Received Accepted Available Keywords Solidification Mechanical Crack Laser Aluminum behavior Results intensity Higher helps 1 Introduction Mechanical constraints are commonly applied during welding process to maintain good fitting between base metals and suppress welding deformation The influences of mechanical constraints on residual Bag for 2005 also process in straint increase process tail that cation that tiation F xhtang of aluminum alloy In their study the constraint intensity was represented by the distance from the weld line to the constraint and the shorter the distance the higher the constraint intensity would be No explanation has been given to the above contradicting conclusions Until now the behavior of weld solidification cracking http dx doi org 10 1016 j jmatprotec 2014 11 037 0924 0136 stress and deformation were investigated by Desai and 2014 Abid and Siddique 2005 and Jing et al 2012 Except the effects of mechanical constraints mentioned above Cross pointed out that the applied mechanical constraints would affect the behavior of solidification cracking during welding Liu 1995 indicated that the transverse mechanical strain the vicinity of weld pool would be larger with the applied con which means the solidification cracking sensitivity would with constraint Dong et al 2005 developed a welding model and analyzed the changes of mechanical strain at the of weld pool with and without constraint The results showed the constraint would promote the formation of weld solidifi cracking However Bollinghaus and Cross 2006 concluded the high levels of constraint intensity appeared to prevent ini and propagation of solidification cracking for welded joint Corresponding author Tel 86 21 34202814 fax 0086 2134202814 E mail addresses welder4302 X Wang Lfg119 Lu hui ping wang H P Wang haichaocui H Cui X Tang wuyixiong Y Wu under mechanical constraint conditions is still not well understood as reported by Coniglio and Cross 2013 The aim of this work was to investigate the relationship between constraint conditions and weld solidification cracking behavior during laser welding of aluminum alloys A carefully designed experimental procedure was carried out to study the solidification cracking behavior with different constraint intensities A thermal mechanical model was proposed to calculate the mechanical strain and accumulated displacement for different parameters The influ ence of mechanical constraints intensity on crack behavior in single side and double side constraint conditions was discussed based on the experimental observations and numerical analysis of transient stress strain conditions 2 Experimental procedure 2 1 Welding setup AA6013 T6 specimen with size of 150 mm 125 mm 2 5 mm was used in the experimental test The chemical composition of AA6013 T6 is listed in Table 1 AA6013 is prone to hot cracking 2014 Elsevier B V All rights reserved Shanghai Key Laboratory of Materials Laser Processing and Modification School of Materials 200240 China General Motor Research on the other hand the friction between the applied constraint and specimen would inhibit transverse displacement The final displacement at the crack tip the competition results of those two opposite effects In single constraint condition the tensile stress plays a main role and increases the transverse displacement at crack tip as shown Fig 7 Compared to no constraint single side constraint case increase crack propagation possibility Fig 14 illustrates the influence of double side constraint con Compared to no constraint case the double side constraint could result in extra mechanical strain due to the preven effect on weld metal contraction The total mechanical strain in for double side constraint is larger than no constraint case and crack initiation possibility for double side constraint increases influence of double side constraint on crack propagation is also by the competition results between the outward tensile and the friction force induced by applied constraints For constraint condition the friction force plays a major since the transverse displacement in BTR decreased seriously the usage of double side constraint as shown in Fig 12 So double side constraint could obviously prevent the propagation of centerline solidification cracking Conclusions The effects of constraint intensities on initiation and propaga of centerline solidification cracking were studied in single side double side constraint conditions respectively The main con are summarized as follows Thermal mechanical models on crack initiation and propaga tion are developed Based on the numerical models mechanical strain and accumulated displacement are proved to be effective indicators for crack initiation and propagation Larger mechan ical strain and accumulated displacement in BTR means the higher possibility of crack initiation and propagation Compared to no constraint case the single side constraint con dition promotes the initiation and propagation of centerline solidification cracking and increasing the constraint intensity would further enhance the promotion effects The double side References Abid M Siddique M 2005 Numerical simulation of the effect of constraints on welding deformations and residual stresses in a pipe flange joint Model Simul Mater Sci Eng 13 919 933 Bollinghaus T Cross C E 2006 The effect of restraint on weld solidification cracking in aluminum Weld World 50 51 54 Coniglio N Cross C E 2013 Initiation and growth mechanisms for weld solidifica tion cracking Int Mater Rev 58 375 397 Cicala E Duffet G Andrzejewski H Grevey D Ignat S 2005 Hot cracking in Al Mg Si alloy laser welding 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