## 3 Results  
### Chemical Analyses  
The weld metal compositions for the two scenarios, without metal powder addition (BC) and with metal powder addition (MP6), are summarised in Table 3. The SEM micrograph in Figure 1 and EDS analyses in Table 4 confirm the alloying of the weld metal with Ni and Al. The area selected for EDS analyses as shown in Figure 1 is positioned at the geometric centre of the weld metal cross section.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline  & **\%C** & **\%Si** & **\%Mn** & **\%O** & **\%Al** & **\%P** & **\%S** & **\%Ti** & **\%Cu** & **\%Cr** & **Balance** \\ \hline Plate & 0.120 & 0.155 & 1.340 & 0.0007 & 0.067 & 0.019 & 0.007 & 0.005 & 0.030 & 0.160 & Fe \\ Wire & 0.110 & 0.137 & 0.990 & 0.0003 & 0.000 & 0.009 & 0.023 & 0.000 & 0.140 & 0.000 & Fe \\ \hline \end{tabular}
\end{table}
Table 1: Base plate and weld wire compositions (mass%).  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline
**MnO** & **CaO** & **SiO2** & **Al2O3** & **CaF2** & **MgO** & **FeO** & **TiO2** & **Na2O** & **K2O** \\ \hline
6.8 & 0.1 & 19.6 & 24.9 & 17.9 & 22.2 & 2.4 & 1.0 & 1.6 & 0.2 \\ \hline \end{tabular}
\end{table}
Table 2: Flux bulk chemical composition (mass%).  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline  & **\%C** & **\%Si** & **\%Mn** & **\%O** & **\%Al** & **\%P** & **\%S** & **\%Ni** & **\%Cr** \\ \hline Base Case & 0.110 & 0.260 & 1.300 & 0.0499 & 0.032 & 0.022 & 0.011 & 0.005 & 0.110 \\ MP6 & 0.111 & 0.390 & 1.653 & 0.0247 & 3.737 & 0.026 & 0.040 & 6.956 & 0.173 \\ \hline \end{tabular}
\end{table}
Table 3: Weld metal compositions (mass%).  
The slight increase in silicon and manganese content of the MP6 weld metal confirms that some aluminothermic reduction of SiO\({}_{2}\) and MnO from the flux occurred via the reactions displayed in Equations (2) and (3). The ppm O is also significantly lowered from 499 ppm O to 247 ppm O due to the de-oxidiser effect of aluminium at the weld pool-slag interface [24, 25, 26, 27, 28].  
Therefore, the MnO and SiO\({}_{2}\) in the slag were reduced by aluminium powder via reactions (2) and (3) as shown below. The FeO in the slag formed from excess oxygen transferred from the arc cavity, is also reduced by aluminum powder via reaction (4) to control the oxygen potential at the weld pool-slag interface [24, 25, 26, 27, 28].  
\[3(\mathrm{SiO_{2}})+4(\mathrm{Al}) = 3(\mathrm{Si})+2(\mathrm{Al_{2}O_{3}})\qquad\Delta H_{2000^{ \circ}\mathrm{C}}^{\mathrm{\ }}= -82.1\mathrm{kJ}/\mathrm{mol\ Al} \tag{2}\] \[3(\mathrm{MnO})+2(\mathrm{Al}) = 3(\mathrm{Mn})+(\mathrm{Al_{2}O_{3}})\qquad\Delta H_{2000^{ \circ}\mathrm{C}}^{\mathrm{\ }}= -248.4\ \mathrm{kJ}/\mathrm{mol\ Al}\] (3) \[3(\mathrm{FeO})+2(\mathrm{Al}) = 3(\mathrm{Fe})+(\mathrm{Al_{2}O_{3}})\qquad\Delta H_{2000^{ \circ}\mathrm{C}}^{\mathrm{\ }}= -416.5\ \mathrm{kJ}/\mathrm{mol\ Al} \tag{4}\]  
( ): liquid.  
The increased percentage of silicon and manganese in the MP6 weld metal, as compared to the base case (BC) weld metal, confirms that sufficient contact time was established between Al powder and flux to enable reactions (2) and (3) to forward to a significant extent. The Al\({}_{2}\)O\({}_{3}\) products formed from reactions (2) and (3) were absorbed into the molten flux since these reactions occurred at the molten flux-weld pool interface [24, 25, 26, 27, 28].