# Failure Response of Simultaneously Pre-Stressed and Laser Irradiated Aluminum Alloys
## 2 Materials and Methods  
The tested materials were purchased from ASM Aerospace Specification Metals Inc. (Pompano Beach, FL, USA). The materials' chemical composition and main properties provided by the supplier are reported in Tables 1 and 2, respectively. The Al-based alloys under test are 6061-T6 and 7075-T6, where T6 means that the alloy is heat treated and artificially aged. Aluminum alloy 6061-T6 (Al-6061) is one of the most extensively used of the 6000 series aluminum alloys. It is a versatile heat-treatable extruded alloy with medium to high strength capabilities and excellent corrosion resistance. It is largely used in aircraft and aerospace components, transport and structural applications [14]. The chemical composition of the Al-6061 is given in Table 1. The major alloying elements are magnesium and silicon. Aluminum alloy 7075-T6 (Al-7075) is a high-strength alloy with strong corrosion resistance. It is widely used in the aircraft and aerospace industries for highly-stressed structural parts [15]. The chemical composition of the Al-7075 is also given in Table 1. The major alloying elements are zinc and magnesium. For the experiments, rectangular strip-shaped specimens with dimensions of 150 \(\times\) 10 \(\times\) 2 mm\({}^{3}\) were used. The specimen dimensions were chosen in accordance with ASTM-B557 specifications and from available literature [16; 18; 19]. The physical and mechanical properties of the investigated alloys are reported in the Table 2.  
Before performing the experiments, the room temperature ultimate tensile strengths of both types of specimens were measured by using the JVJ-505 universal tensile testing machine (SIOMM, Shanghai, China). The resulting average values of room temperature yield strength and ultimate tensile strengths for Al-6061 and Al-7075 alloys are given in Table 2. Experiments were performed for 85% of ultimate tensile strength in each case, but with varying preloaded speeds of 0.5, 1, 2 and 4 mm/min, respectively. The specified preload was provided on the specimen by the JVJ-505 universal testing machine by pre-setting the loading speed. Tensile loading experiments were designed in accordance with the ASTM-B557 standards, while the preloaded speeds were obtained from the literature [19]. After reaching 85% of ultimate tensile strength, the specimens were kept under a constant loading state. The predetermined constant preload values were 6.85 kN (340 MPa) and 12.1 kN (514 MPa) for Al-6061 and Al-7075, respectively. The loading profile was chosen to examine the effect of loads on the observed behavior. However, in the following results of Figures 1 and 2, the first loading part (before reaching the determined preload) of the curves was cut, and corresponding curves only represent the specimens after reaching the constant preloaded state. In Table 3, the test conditions of laser power densities and loading speeds are given. The laser began to irradiate the specimens while they were being held under a constant prescribed loading state. The distance between the laser emitter and the specimen was 60 cm. The laser spot with a 7-mm diameter was perpendicularly focused on the center of the specimen, with four laser power densities of 1.1, 1.6, 2.2 and 2.7 kW/cm\({}^{2}\) respectively employed in the test. The CW ytterbium (Yb) fiber laser (RFL-C1000, Raycus, Wuhan, Hubei, China) with a 1080-nm wavelength and 1 kW maximum power was used for laser irradiation. The specimens were continuously irradiated until \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline
**Alloy** & **Si** & **Fe** & **Cu** & **Mn** & **Mg** & **Zn** & **Ti** & **Cr** & **Ni** & **Pb** & **Al** \\ \hline Al-6061 & 0.62 & 0.46 & 0.29 & 0.09 & 0.88 & 0.04 & 0.05 & 0.17 & 0.01 & & Bal. \\ Al-7075 & 0.09 & 0.22 & 1.52 & 0.12 & 2.42 & 5.72 & 0.06 & 0.19 & & 0.02 & Bal. \\ \hline \end{tabular}
\end{table} 
Table 1: Chemical composition of Al alloys in weight % [16; 17]. (Bal: Balance)