Effect of annealing temperature and cutting angle of specimens on metallurgical and mechanical properties of Mg-7Li-1Zn alloy via Taguchi approach and response surface analysis

The main aim of this research is to assess the effect of annealing temperature and cutting angle of specimens on the metallurgical and mechanical properties of superlight Mg-Li-Zn alloy thin sheets. To this end, as-rolled LZ71 (Mg-7%Li-1%Zn) alloy was annealed at different temperatures (0, 250, and 350° C) for 3 hours. After that, the test specimens were cut at different angles relative to the rolling direction (0, 45, and 90 °). Next, several experiments were accomplished to study the microhardness, microstructure, grain size, and tensile behavior of the LZ71 alloy. Finally, different Design of Experiment (DOE) techniques were used to determine the individual and interaction effects of annealing temperature and cutting angle of specimens on the material characterization of LZ71 alloy. In this regard, annealing temperature and cutting angle were considered as input parameters in both Taguchi Approach (TA) and Response Surface Analysis (RSA). Also, key parameters of the tensile test including Ultimate Tensile Strength (UTS), Yield Stress (YS), Elastic Modulus (EM), and Strain at BreakPoint (SBP) were considered as outputs. It was concluded that annealing temperature influence on the static behavior of LZ71 alloy is several times greater than the effect of cutting angle (i.e., the effect of annealing temperature on the UTS, YS, EM, and SBP is 92%, 76%, 61%, and 66%, respectively). Moreover, the results of the Response Surface Optimization Algorithm (RSOA) showed that to achieve the best static properties in different directions, the annealing temperature should be selected to be 350°C.