# Effect of Heat Input on LMHMW Joint of Carbon Steel
## 2 Experimental Materials and Methods  
LMHMW with laser leading is schematically demonstrated in Figure 1. The chemical composition of the base metal and consumable electrode adopted in this investigation are shown in Tables 1 and 2, respectively. A single V groove butt weld in the IG position was employed in the current experiment, and detailed dimensions of joint design are presented in Figure 2a,b.  
Figure 1: Schematic diagram of laser-MIG hybrid welding.  
The equipment used in this research consists of a TrumpF 12 kW Disk Laser (TruDisk12003) with wavelength 1030 nm and 300 um focused spot diameter. A six-axis KR30 HA Kuka robot with a maximum reach of 2033 mm was coupled with laser welding for automating the whole process. A Fronius multiprocess Transplussynergic (TPS 5000) having a maximum current carrying capacity of 500 Amps was exploited for MIG welding. Inert Argon shielding gas with 99.99% purity level at a 15 L/min flow rate was directed at the common interaction zone of arc and laser heat source.  
A total of 5 specimens under varying heat inputs were welded, and the welding process on each 20 mm thick sheet was accomplished in three layers, as elaborated earlier in Figure 2c. The detailed welding parameters are shown in Table 3. Heat input can be expressed by the following equation [23]:  
\[E=\frac{P_{L}+P_{A}}{v}=\frac{P_{L}+U\cdot I}{v} \tag{1}\]  
where \(E\) is heat input (KJ/cm), \(v\) is the welding speed (cm/s), \(P_{L}\) and \(P_{A}\) represent the laser and arc power (Watts), respectively. \(U\) and \(I\) denote arc voltage (V) and current (A), respectively.  
Oil on the faying surfaces of the base metal was cleaned with acetone. An austenitic stainless steel wire brush was used to remove the oxide layer during interpass cleaning. No preheating or interpass temperature controls were enforced because of the very low carbon equivalent of Q235 steel. After welding, transverse metallography samples were extracted from the specimen to observe interfacial microstructure. Samples were ground and polished using progressively finer abrasive grit, and diamond paste for mirror finishing with subsequent etching in 0.5% nital solution for 8 s. Macroscopic morphology and interfacial microstructure was characterized by an Optical microscope. The microhardness of samples was measured by the Vickers microhardness tester (HVS-50) (Nanjing, China) using a 10 kg load and a dwell period of 15 s. Tensile test samples are prepared by wire EDM and tested on a Universal testing machine (CMT5305), (Shanghai, China), having a maximum capability of 300 kN force.  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Steel** & **C** & **Si** & **Mn** & **S** & **P** & **Fe** \\ \hline Q235 & 0.16 & 0.21 & 0.55 & 0.02 & 0.03 & Bal. \\ \hline \end{tabular}
\end{table}
Table 1: Chemical composition of workpiece [Mass fraction/%].  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Consumable Electrode** & **C** & **Si** & **Mn** & **Ti** & **Fe** \\ \hline JM-68 & 0.07 & 0.58 & 1.76 & 0.12 & Bal. \\ \hline \end{tabular}
\end{table}
Table 2: Chemical Composition of the JM-68 [Mass fraction/%].  
Figure 2: Schematic diagram: (**a**) Dimensions of the workpiece; (**b**) Sizes of the groove; (**c**) weld cross-section.