## Materials and Experimental Procedure  
### Materials  
The experimentation was performed on samples of AlMg3 aluminum alloy (EN AW-5754, UNS A95754, 51000), St37-2 low-carbon steel (EN S235 JR, ASTM A283C, 1.0037) and AISI 304 stainless steel (EN X5 CrNi18-10, AISI 304, 1.4301). The chemical composition and properties declared by the manufacturers are reported in Tables 1 and 2, respectively. Aluminum and its alloys exhibit a high strength-to-weight ratio, corrosion resistance and weldability. Given to their considerable properties, Al-alloy sheets are used to produce structural parts for industrial applications in aeronautic, automotive and other relevant technological fields. Aluminum alloys are cut with the use of inert gas, usually nitrogen. More specifically, AlMg3 is an aluminum-magnesium alloy (5 xxx series), suitable for cold-forming and welding, which exhibits better corrosion resistance and higher mechanical properties than pure aluminum. As for pure aluminum, AlMg3 is characterized by high thermal conductivity. Heat transfer plays a critical role in laser cutting performance. Since thermal conductivity refers to the rate at which heat is removed from the cutting area, low thermal resistance increases heat dissipation, resulting in lower energy available to the machining and, consequently, higher energy consumption and loss of efficiency. Moreover, heat removal may result in cooling of the molten metal on the underside of the kerf, tapered edge and slag formation [18]. Furthermore, light reflective metals, such as aluminum alloys, may reduce the maximum cutting speed and require more power density to initiate the cut [5]. Steel and its alloys are widely employed in many industries because of their combination of strength and ductility. Steel is typically cut by using oxygen as assisting gas. St37-2 is a structural carbon steel characterized by relatively low hardness and prone to corrosion. Experimentally it was found that the thermal power contribution released by the oxidation reactions of steel is about equal to the power provided by the laser beam (per unit of length). As a result, it is possible to increase the cutting speed or the thickness of metal being cut. Furthermore, the use of oxygen as an assisting gas introduces an element of complexity into the laser cutting of low-carbon steel. In oxygen-assisted laser cutting, the laser beam heats the material to the ignition temperature, and forced burning of iron in oxygen occurs. Therefore, the end product quality depends on the thermal balance of two distinct cutting fronts. When the reaction front dominates, the cutting process results in poor surface quality (side burning). \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**AlMg3** & **Al** & **Mg** & **Mn** & **Si** & **Cr** & **Zn** & **Ti** & **Cu** & **Fe** & **Residuals** \\ \hline Min (\%) & 94.2 & 2.6 & - & - & - & - & - & - & - & - \\ Max (\%) & 97.4 & 3.6 & 0.5 & 0.4 & 0.3 & 0.2 & 0.15 & 0.1 & 0.4 & 0.15 \\ \hline St37-2 & \multirow{2}{*}{Fe} & \multirow{2}{*}{C} & \multirow{2}{*}{Mn} & \multirow{2}{*}{S} & \multirow{2}{*}{P} & \multirow{2}{*}{residuals} \\ UNI EN 10025 & & & & & & & & & \\ Max (\%) & 98.13 & & 0.21 & 1.50 & 0.055 & 0.055 & 0.05 \\ \hline AISI 304 & \multirow{2}{*}{Fe} & \multirow{2}{*}{C} & \multirow{2}{*}{S} & \multirow{2}{*}{P} & \multirow{2}{*}{Mn} & \multirow{2}{*}{Si} & \multirow{2}{*}{N} & \multirow{2}{*}{Cr} & \multirow{2}{*}{Ni} & \multirow{2}{*}{residuals} \\ UNI EN 10088-1 & & & & & & & & & \\ Min (\%) & 75 & - & - & - & - & - & 17 & 8 & - \\ Max (\%) & 66.57 & 0.07 & 0.15 & 0.045 & 2 & 1 & 0.11 & 19.5 & 10.5 & 0.05 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Chemical composition of the adopted materials.