I had the same problem. Solved it by using a javascript library called FileSaver
Just call
saveAs(file, 'filename');
Full http post request:
$http.post('apiUrl', myObject, { responseType: 'arraybuffer' })
.success(function(data) {
var file = new Blob([data], { type: 'application/pdf' });
saveAs(file, 'filename.pdf');
});