asp.net send mail attachment

i cannot add file attachment to mail whitout saving.

adding the file , the added file seems  as .dat.

SmtpClient client = new SmtpClient();
string name = adsoyadik.Text;
string birthDay = dogumTarihik.Text;
string birthPlace = dogumYeriik.Text;
string gender = cinsiyetik.SelectedItem.ToString();
string situation = medenihalik.SelectedItem.ToString();
string mobile = telik.Text;
string email = epostaik.Text;
string address = evadresik.Text;

MailMessage ikgonder = new MailMessage();
ikgonder.To.Add("xx@xxx.xxx.xx");
ikgonder.From = new MailAddress("xxx@xxx.xxxx.xx", "Akdeniz Analiz-İş Başvuru Formu");
ikgonder.Subject = adsoyadis.Text + "xxxxxxxxxx.xxxxxxx";
ikgonder.IsBodyHtml = true;
NetworkCredential guvenlik = new NetworkCredential("xxx@xxx.xxxxx.xxx", "xxxxxxx");
client.Credentials = guvenlik;
client.Port = 587;
client.Host = "xxxxxx.xxxxxxx.xxxxxx.xxxxxxx";

ikgonder.Body = "<b><br>AKDENİZ ANALİZ - İş Başvuru Formu <br><br></b>Ad Soyad: " + name + "<br><br>Doğum Tarihi: " + birthDay + "<br><br>"
+ "Doğum Yeri: " + birthPlace + "<br><br>" + "Cinsiyetiniz: " + gender + "<br><br>" + "Medeni Hali: " + situation + "<br><br>" + "Cep Telefonu: " + mobile + "<br><br>" + "E-posta Adresi: " + email + "<br><br>" +
"Ev Adresi: " + address + "<br>";
;

ikgonder.Attachments.Add(new Attachment(FileUpload1.FileContent, System.IO.Path.GetFileName(FileUpload1.FileName)));

client.Send(ikgonder);