Does a divorce take effect if a husband tells his wife, "If you leave the house without a hijab, you will be divorced," and she later leaves without a hijab, knowing that his intention was not to divorce her but to frighten her?

The statement "you will be divorced" is a promise of divorce, not an actual divorce. Divorce does not occur through it, even if the phrasing is repeated many times. There is no obligation to fulfill this promise, nor is it recommended. Therefore, nothing is consequential from this statement, even if the condition it was contingent upon is met.