formation. Introduction To study the hybrid laser/GMA welding of aluminum alloys (AA6061 and AA5456) to Armor steels (MIL-DTL and MIL-DTL ) by using Triclad insert in a T-joint configuration. To study the effect of the off-set distance between laser and arc on the temperature field by a finite element numerical method. To optimize and control the processing parameters in the hybrid laser/arc welding process. Objectives Thermal and Mechanical ModelingExperimental procedure: Hybrid Laser/GMAW System Solder Experimental and Numerical Studies on the Hybrid Laser/GMAW Welding Process for Joining Dissimilar Materials PhD students: Mehdi Mazar Atabaki; Wei Liu, Research Engineer: Dr. Junjie Ma, Advisor: Prof. Radovan Kovacevic Organization: Bobby B. Lyle School of Engineering, Southern Methodist University, Dallas, Texas Substrate Solder Pad Solder Conclusions: Aluminum Alloys (AA6061 and AA5456) have been successfully welded to the two Armor steels (MIL-DTL and 12560) by using a Triclad insert in a double grooved T-joint configuration by a Hybrid/laser arc welding process. The Triclad insert, consisting of steel SA516 and aluminum AA 5456, was made by an explosive welding process. The welding parameters were optimized in order to avoid excessive overheating at the specified distance from the weld and an intensive experimentation was performed in order to determine the optimal welding parameters of the hybrid laser/arc welding of the aluminum alloy. Under similar experimental conditions for HLAW of the aluminum alloys, the penetration depth of the coupons provided by AlSi filler was around 20 % higher than the coupons prepared with the AlMg filler metal. This different behavior is associated with the thermal properties, which depend on the total amount of alloying elements. In addition, amount of spattering during the hybrid welding was increased in the case of AlMg alloy. A three-dimensional finite element model has been introduced to study the temperature distribution and weld pool geometry in the hybrid laser/arc welding of dissimilar materials. The simulation and experimental results show that when the separation distance between the arc and laser is in the critical range (8 mm-14.5 mm), the plasma arc and the laser act at the different locations and the concentration of the arc increases, causing the increase in the penetration depth, higher heat input and the overall volume of the weld pool. Hybrid laser arc welding of different aluminum alloys (AA 5456 and AA 6061) and steel grades (MIL and MIL 14600) were studied by experimental and numerical investigations. The numerical simulation has been considered by using two double-ellipsoidal heat sources for the gas metal arc welding and laser welding. The offset distance of the metal arc welding and laser showed a considerable influence on the molten pool geometry, the heat distribution and penetration depth during the bonding process. The experiments indicate that the laser power, arc voltage and type of the filler metal can effectively determine the final properties of the joints. The numerical simulation was verified by the experimental results. Research results Future Work: A series of experiments on hybrid laser/arc welding will be performed to validate the thermo-mechanical analysis. The microstructural and mechanical properties of the joints will be studied. On line monitoring of the hybrid/laser arc welding will be performed for the full coverage on the joining of aluminum alloys and steel grades. Governing Equation: Heat input Heat loss due to convection and radiation Experimental setup Flowchart of numerical procedure no Build up the CAD model of welded joint and define thermal physical properties Choose the element type and meshing: a finer mesh locates at the weld zone Define the thermal boundary condition and calculate the temperature field START Is thermal analysis accurate enough compared to experiments? Define the mechanical constraint and calculate the transient stress and strain yes Switch the element type to mechanical analysis, delete all the thermal boundary condition, and chose the reasonable mechanical material model Is mechanical analysis accurate enough compared to experiments? Output the numerical results and simulation is finished yes no Hybrid laser/arc welding process for joining dissimilar Aluminum Alloys and steel grades D Laser Beam GMAW torch keyhole Molten pool PC Magnification Len Narrow band-pass filter-532 nm Focus Len High speed CCD camera Green laser as illumination light SUBSTRATE Schematic of Machine vision D --- distance between laser beam and GMAW torch (a) In an adequate distance between arc and laser (D) the laser beam energy can be efficiently absorbed by the welded material and (b) the CCD Camera and spectroscopy for the verification of the molten pool shape and plume formation. Close-up of the hybrid laser/arc welding setup before joining in z-y plane (a) (b) Laser power: 3.7 KW; The welding speed: 6 mm/s; Wire feed rate: 12 m/min; voltage: 32 V; Base current: 35 A; Pulse time: 1.9 ms; Pulse shape: steep; Dx: 14.5 mm; Vd: 16 mm, Shoulder width: 0.1 mm. HLAW of AA6061 and AA5456 HLAW of MIL-DTL and A516 Mechanism of HL/AW