Experimental and Statistical Study of the Effect of Heat Treatment on Mechanical Properties and Surface Roughness of Thin-Walled Samples Obtained by Selective Laser Melting from Al-Mn-Mg-Ti-Zr Alloys

Manufacturing aluminum alloy by selective laser melting (SLM) is actively imple-mented in various industries, allowing to reduce the cost of the final product and the time to market. Despite the long existence of the technology, there are still problems associated with improving the quality of SLM products, particularly those with thin walls. The purpose of our work is to study the effect of heat treatment temperatures at temperatures from 260 ºC to 530 ºC for one hour on the tensile mechanical properties, hardness and surface roughness of thin-walled samples made by selective laser melt-ing technology from Al-Mn-Mg-Ti-Zr alloy. Monte Carlo statistical analysis and mod-eling methods were used as the main method of theoretical research. Statistical analysis of the surface roughness of thin-walled specimens manu-factured by SLM technology showed that there were no statistically significant dif-ferences (p-value>0.05) in the specimens before heat treatment and after heat treat-ment. However, data separation by hierarchical clustering method allowed us to es-tablish the presence of strong correlations between roughness parameter Rz and mi-crohardness in the group of samples heat-treated at 530 ºC. The construction and analysis of the centrality of the correlation graphs shows that the parameter with the largest number of statistically significant correlations changes with increasing heat treatment temperature. At temperatures up to 290 ºC the parameter with the largest number of correlations is the strain hardening coefficient, at temperatures from 320 ºC to 500 ºC the Young's modulus becomes the most significant, and at 530 ºC - Rz after heat treatment. The analysis of regression equations for predicting the strain hardening coefficient, Young's modulus and Rz after heat treatment with maximum centrality showed that of all mechanical properties considered in our work, the strength limit, strain corresponding to the strength limit, Young's modulus, modulus along the secant of 0.05% - 0.25% strain and strain hardening coefficient are the most significant. Mod-eling of these values depending on the heat treatment temperature with subsequent validation of the results showed that the new approach to the prediction of physical quantities presented in our work based on the Monte Carlo method gives a better prediction of the experimental results, compared to the empirical equations based on robust regression the only exception is the prediction of the strain hardening coeffi-cient. Metallographic and X-ray phase analysis in conjunction with the results of sta-tistical analysis showed that at increasing the temperature of heat treatment mi-cropores (macrodefects) shift to the boundary of the melt zones with subsequent exit to the surface, which together with the formation of intermetallic phase and the release of titanium and zirconium leads to strain hardening of thin-walled samples obtained by selective laser melting of Al-Mn-Mg-Ti-Zr alloy. As a result of this work, it was found that the maximum strain hardening of thin-walled specimens obtained by selective laser melting technology from Al-Mn-Mg-Ti-Zr alloy is achieved at a heat treatment temperature of 530 ºC within an hour, and the mechanism of hardening has a dual character of dispersion and due to the reduction of macro-defectivity.