A thin and large high toughness die-cast product is provided that is formed from an Al--Mg casting alloy having the composition 3.5 wt %.ltoreq.Mg.ltoreq.4.5 wt %, 0.8 wt %.ltoreq.Mn.ltoreq.1.5 wt %, Si<0.5 wt %, Fe<0.5 wt %, a sum (Ti+Zr) of amounts of Ti and Zr added of equal to or greater than 0.3 wt %, and a ratio (Ti/Zr) of the amounts of Ti and Zr added of at least 0.3 but not more than 2, with the balance being Al.