You are doing this:
comboBox1.DisplayMember = "alloyName";
comboBox1.ValueMember = "alloyName";
comboBox1.DataSource = dt;
which "alloyName" is not existed.
You can type this in stead:
comboBox1.Items.Clear();
foreach (DataRow dr in dt.Rows)
{
comboBox1.Items.Add(dr[0] + "");
}