Angular2 file download with Asp.Net MVC is always named 'download.xlsx' - how do I change the name?

Controller method:

public FileResult FromModel(ExcelWorkBook model)
{
    byte[] fileBytes;
    var reportStream = ExcelCreator.Create(model);
    try
    {
        fileBytes = reportStream.ToArray();
        var fileName = "some_crazy_filename.xlsx";

        var encoding = System.Text.Encoding.UTF8;
        Response.Charset = encoding.WebName;
        Response.HeaderEncoding = encoding;
        Response.AppendHeader("Content-Disposition", new System.Net.Mime.ContentDisposition { FileName = fileName, Inline = true }.ToString());
        return File(fileBytes, "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet");
    }
    catch (Exception) { throw; }
    finally
    {
        reportStream.Close();
        reportStream.Dispose();
    }
}

Angular2 method:

this.http.post('/Excel/FromModel', postData, { headers: headers, responseType: ResponseContentType.ArrayBuffer })
    .catch(this.handleError)
    .subscribe(x => {
        console.log(x);
        let blob = new Blob([x.arrayBuffer()], { type: 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet' });
        fileReader.readAsDataURL(blob);
        fileReader.onloadend = function (readerEvent) {
            window.open(fileReader.result);
        };
    });

The file is downloaded perfectly, but the filename is always download.xlsx any idea what I am missing? I feel like I am missing something easy... thank you!