What would cause a crack in the edge of an alloy rim(s)......? I ahve two that I have found 2 cracks on right at the inner edge about 5-10mm in length.

Can these be repair and would the integritty of the rim be sacrificed if it was repaired? They are old-ish rims but only just seen the cracks aftre digging them ou of the storage that is my parents lockup.