Magnesium alloys have wide application in aerospace and automotive industries due to their high strength to weight ratio and desired mechanical properties. In this present research, the effects of three input parameters of the wire electrical discharge machining (WEDM) process, including pulse on time, pulse current, and servo feed rate were studied on the performance characteristics namely; material removal rate, kerf width, and surface roughness during machining of AZ91 magnesium alloy. This research is the first comprehensive study of the electrical discharge machining of magnesium alloys and aims to analyses the machinability and behavior of materials with low melting point and high thermal conductivity during WEDM. For this purpose, 15 experiments were designed by the design of experiments technique. Using response surface methodology, mathematical models were developed and the contribution percentage of each variable input parameter on output parameters was found. Analysis of variance results revealed that pulse on time and pulse current have the most effect on process output parameters, respectively, while the effect of the servo feed rate was insignificant. The experimental results showed that the material removal rate and the kerf width during the WEDM of magnesium is considerably higher than hard materials and it can be reached to about 180 mm 3 min −1 while kerf width and surface roughness are about 0.450 and 4.683 μm, respectively. Despite the high cutting rate, the surface roughness is appropriate and comparable to hard materials, indicating high machinability of magnesium alloys by WEDM. To study the surface topography and microstructural changes, atomic force microscope, scanning electron microscope and EDX analysis have been used. SEM micrographs show that the number of microcracks, indicating the surface damage, is low in the machined surface which shows WEDM capability in producing nondamaged work surfaces. The maximum recast layer thickness is about 6.91 μm and minimum is 3.09 μm.

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