Process for forming medium-strength heat-resistant magnesium alloy thick plate

The invention discloses a process for forming a medium-strength heat-resistant magnesium alloy thick plate with the thickness of 50-80mm. The process route comprises the following steps: big furnace smelting, semi-continuous casting, homogenizing annealing, variable temperature multi-directional forging, extrusion forming and aging treatment, wherein the step of variable temperature multi-directional forging is performed on a hydraulic machine, the temperature of the ingot blank is kept at 380-410 DEG C for 3-5 hours before forging, and the pressing speed is 200-400mm/minute; the step of extrusion forming is performed on a horizontal extruder, the temperature of the ingot blank is kept at 340-350 DEG C for 3-5 hours before extrusion, and the thickness plate with the extrusion ratio of 13-15, the extruded thickness of 50-80mm, the width of 130-200mm and the length of more than or equal to 1000mm is extruded. After the aging treatment, the room-temperature yield strength of the thick plate along the extrusion direction is more than or equal to 260MPa, the tensile strength is more than or equal to 370MPa, and the elongation is more than or equal to 9 percent. The process is high in forming efficiency, and large-scale industrial production can be realized.