Text alignment in DataGrid

I'm programming by WPF. I need a way to make center content of cells, in DataGrid control. I use this code also:

<DataGrid x:Name="dg1" HorizontalAlignment="Left" Margin="10,10,0,0"
    VerticalAlignment="Top" Height="360" Width="498"
    FontFamily="2  Badr" FontSize="18" 
    AlternatingRowBackground="LightCoral" FlowDirection="RightToLeft"
    HorizontalContentAlignment="Center" VerticalContentAlignment="Center" 
    Background="{x:Null}"/>

What is wrong?

You need set DataGridCell style

    <DataGrid>
        <DataGrid.Columns>
            <DataGridTextColumn>
                <DataGridTextColumn.ElementStyle>
                    <Style TargetType="TextBlock">
                        <Setter Property="HorizontalAlignment" Value="Center" />
                    </Style>
                </DataGridTextColumn.ElementStyle>
            </DataGridTextColumn>
        </DataGrid.Columns>
    </DataGrid>

For those who need to format only one dynamic DataGrid column in VB.NET from a custom XAML style:

In Application.xaml:

<Application.Resources>
    <ResourceDictionary>
        <Style x:Key="DataGridCellCentered" TargetType="DataGridCell">
            <Setter Property="TextBlock.TextAlignment" Value="Center" />
        </Style>
    </ResourceDictionary>
</Application.Resources>

In VB.NET code:

Me.MyDataGrid.Columns(5).CellStyle = TryFindResource("DataGridCellCentered")

Regards!