Glass compositions that retain high compressive stress after post-ion exchange heat treatment

An alkali aluminosilicate glass comprising at least about 50 mol % SiO2, at least about 10 mol % Na2O, and MgO, wherein the alkali aluminosilicate glass is free of at least one of K2O, B2O3, CaO, BaO, and P2O5, wherein the alkali aluminosilicate glass has a thickness t of up to about 1 mm, is ion-exchanged, and has a compressive layer extending from a surface of the alkali aluminosilicate glass to a depth of layer of up to about 70 μm and a maximum compressive stress of at least about 950 MPa at the surface, and wherein the alkali aluminosilicate glass experiences a weight loss of less than or equal to about 0.030 mg/cm2 after immersion in an acid solution at 95° C. for about 7 hours, the acid solution comprising about 5 wt % HCl.

A method of ion exchanging an alkali aluminosilicate glass, the method comprising the steps of:

• a. ion exchanging the alkali aluminosilicate glass in an ion exchange bath comprising a potassium-containing salt, wherein the ion-exchanged alkali aluminosilicate glass has a compressive layer having a compressive stress at a surface of the alkali aluminosilicate glass of at least about 950 MPa and a depth of layer of a compressive layer of about 0.25t or less, the compressive layer extending from the surface to the depth of layer;
• and
• b. heat treating the ion-exchanged alkali aluminosilicate glass at a temperature of at least about 400° C., wherein the compressive stress at the surface of the on exchanged alkali aluminosilicate glass after the heat treating step is at least about 600 MPa.