[Artur_Hopf]

Вот так получилось:

var post = [
        {
            'test1': 1,
             'test2': 2
        },
        {
           'test1': 3,
           'test2': 4
        }
    ];
    var formData = new FormData(),
        request = new XMLHttpRequest();
     
    [].forEach.call(post, function(item, i) {
        for (key in item) {
            formData.append('post[' + i + ']['+key+']', item[key]);
        }
    })
     
    request.open("POST", "post.php");
    request.send(formData);