Aluminium Alloy Plate Having Excellent Forming Property

The invention provides an AL-Mg alloy plate having excellent forming property. The AL-Mg alloy plate has no problem of decreasing bending performance caused by age-hardening in room temperature, and low appearance of SS lines. When manufacturing the AL-Mg alloy plate formed by constitutions containing specific Mg and Cu, not only the cooling speed of quenching processing after solution treatment is controlled periodically, but also additional annealing conditions are controlled, thereby a plate tissue existing as Cu cluster, hard to disffuse as Mg, and hard to appear in a zigzag shape that indicated by a heat absorption peak height between 180 to 280 DEG C of a heating curve stating from the room temperature obtained through a differential thermal analysis of the alloy plate to suppress the appearance of the forcing and forming SS lines.