Steels In Lap Joint Configuration Research Articles

Fundamental study of blue wavelength laser for welding low thickness dissimilar Cu and steel materials

The present study reports on the application of blue wavelength (450 nm), continuous wave laser welding of Ni-coated copper to mild steel in lap joint configuration. The laser power was varied from 1 kW to 1.5 kW in incremental steps of 0.1 kW whilst the welding speed was kept constant at 6 m/min. Metallographic examination of the weld samples revealed that the weld penetration and width strongly correlated to the laser power, the characteristic of a stable welding process due to the high absorption of the blue wavelength laser. No substantial cracks or a large number of porosities were observed in the welds. The mechanical properties of the weld samples were characterized through tensile testing and microhardness measurements to establish the microstructure property relationship. The maximum tensile strength measured for specified weld geometries was 649 N with corresponding weld efficiency of 91%. The higher-strength welds showed a tensile fracture in the heat-affected zone (HAZ) of Cu, at the periphery of weld nuggets while lower-strength welds showed interfacial fracture due to the lack of fusion. In samples made with sufficient penetration the joint strength was controlled by the HAZ rather than the joint microstructure. A significant increase in the microhardness was measured inside the weld nugget compared to the parent materials, attributed to the formation of Cu-Fe composite microstructure owing to the inter-mixing of Cu and Fe during welding. The highest microhardness was observed in the HAZ of the mild steel due to martensitic microstructure formation in this region.

Effect of position and force tool control in friction stir welding of dissimilar aluminum-steel lap joints for automotive applications

Widespread use of aluminum alloys for the fabrication of car body parts is conditional to the use of appropriate welding methods, especially if dissimilar welding must be performed with automotive steel grades. Friction stir welding (FSW) is considered to be a reasonable solution to obtain sound aluminum-steel joints. In this context, this work studies the effects of tool position and force control in dissimilar friction stir welding of AA6061 aluminum alloy on DC05 low carbon steel in lap joint configuration, also assessing proper welding parameter settings. Naked eye and scanning electron microscopy (SEM) have been used to detect macroscopic and microscopic defects in joints, as well as to determine the type of intermixture between aluminum and steel. The joint strength of sound joints has been assessed by shear tension test. Results point out that tool force control allows for obtaining joints with better quality and strength in a wider range of process parameters. A process window has been determined for tool force conditions to have joints with adequate strength for automotive purposes.

AN EMPIRICAL RELATIONSHIP FOR ESTIMATING METALLURGICAL AND MECHANICAL BEHAVIOR OF RESISTANCE SPOT WELDED DP800 STEEL JOINTS

Similar joints of DP800 (Dual Phase) steel in lap joint configuration were fabricated using resistance spot welding (RSW) process. The process parameters were optimized using DOE (design of experiments) and the welds joints were fabricated using the obtained DOE matrix. The tensile shear fracture load (TSFL) of joints was evaluated using universal testing machine. Microhardness variations across the weld cross-section was recorded using Vickers’s microhardness tester. Microstructural features were analyzed using optical microscopy (OM) and scanning electron microscopy (SEM). From this investigation, it is understood that increase in welding current increases the nugget zone size and it led to increasing the degrease of softening in the HAZ. The tensile shear strength is found to increase with increase in welding current up to a certain limit and then it decreases. The microhardness profile shows a peak hardness in nugget zone and the hardness is lower in the HAZ. The softening of HAZ is mainly attributed to inter-critical heating during welding.

Numerical modelling of gas metal arc joining of aluminium alloy and galvanised steels in lap joint configuration

Advanced pulsed current gas metal arc based processes are increasingly attempted for the joining of aluminium alloys and galvanised steel sheets. The bead profile and the thickness of the interfacial Fe–Al intermetallic (IMC) layer significantly influence the failure strength of these joints. Although several experimental studies have examined the nature and extent of the IMC phases and consequent joint strength, quantitative efforts to estimate bead profile and the IMC layer thickness as function of process conditions and resulting heat input are scarce. We present here for the first time a coupled theoretical and experimental study to estimate the bead profile and Fe–Al IMC layer thickness for joining of galvannealed steel and aluminium alloy sheets in a typical lap joint configuration. The computed values of bead profile and IMC layer thicknesses are validated with the corresponding experimental results.

Real-time monitoring of laser welding of galvanized high strength steel in lap joint configuration

Two different cases regarding the zinc coating at the lap joint faying surface are selected for studying the influence of zinc vapor on the keyhole dynamics of the weld pool and the final welding quality. One case has the zinc coating fully removed at the faying surface; while the other case retains the zinc coating on the faying surface. It is found that removal of the zinc coating at the faying surface produces a significantly better weld quality as exemplified by a lack of spatters whereas intense spatters are present when the zinc coating is present at the faying surface. Spectroscopy is used to detect the optical spectra emitted from a laser generated plasma plume during the laser welding of galvanized high strength DP980 steel in a lap-joint configuration. A correlation between the electron temperature and defects within the weld bead is identified by using the Boltzmann plot method. The laser weld pool keyhole dynamic behavior affected by a high-pressure zinc vapor generated at the faying surface of galvanized steel lap-joint is monitored in real-time by a high speed charge-coupled device (CCD) camera assisted with a green laser as an illumination source.