How to generate code using combobox text

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C#

I want to create a 'code', which is dependent on a combobox selection and I have implemented a random number generator also. So if the user selects Aluminium in the combobox I want a code to be created of 'AL093847', for example. At the moment the code is only being generated for 'Copper' im not sure why. can anyone help

private void button1_Click(object sender, EventArgs e)
{

    Random generator = new Random();
    int r = generator.Next(1000000);
    string rnd = r.ToString("D6");

    string Material = "";

        if (comboBox1.SelectedText == "Iron")
        {
            Number.Text = Number.Text + "FE" + rnd;
        }

        else if (comboBox1.SelectedText == "Aluminium")
        {
            Number.Text = Number.Text + "AL" + rnd;
        }
         else
        {
            Number.Text = Number.Text + "CU" + rnd;
        }


    }

What I have tried:

private void button1_Click(object sender, EventArgs e)
{

    Random generator = new Random();
    int r = generator.Next(1000000);
    string rnd = r.ToString("D6");

    string Material = "";

        if (comboBox1.SelectedText == "Iron")
        {
            Number.Text = Number.Text + "FE" + rnd;
        }

        else if (comboBox1.SelectedText == "Aluminium")
        {
            Number.Text = Number.Text + "AL" + rnd;
        }
         else
        {
            Number.Text = Number.Text + "CU" + rnd;
        }


    }