Elucidating formability limits in warm incremental sheet forming of AZ61 magnesium alloy using integrated grey relational and data-driven analysis

The growing demand for lightweight structural components in the automotive and aerospace sectors has intensified interest in magnesium alloys; however, their limited formability at room temperature continues to restrict widespread industrial adoption. In this study, the formability and surface quality of AZ61 magnesium alloy during warm incremental sheet forming (ISF) are systematically investigated. A straight-groove forming test was conducted using a Taguchi L27 experimental design to evaluate the effects of key process parameters. To simultaneously optimize formability and surface roughness, Grey Relational Analysis (GRA) was employed. Analysis of Variance (ANOVA) of the GRA results revealed that step depth was the most influential parameter, contributing 70.12% to the total variance, followed by spindle speed with a contribution of 12.97%, while tool diameter and feed rate exhibited comparatively minor effects. The optimal parameter combination, 8 mm tool diameter, 700 rpm spindle speed, 0.3 mm step depth, and 500 mm/min feed rate, resulted in enhanced formability and improved surface quality. Forming Limit Diagram (FLD) analysis confirmed an expansion of the safe deformation zone under optimized conditions. Scanning Electron Microscopy (SEM) observations indicated a predominantly ductile fracture mode characterized by deep dimples and fibrous tearing. Furthermore, a Random Forest-based machine learning model corroborated the ANOVA findings, providing additional validation and trend confirmation for the identified parameter influences. The integrated experimental and data-driven framework presented in this work supports the development of intelligent and optimized warm ISF processes for magnesium alloys.