using System.Windows.Forms;
using DevExpress.Utils;
using DevExpress.XtraCharts;
// ...

private void Form1_Load(object sender, EventArgs e) {
    // Cast the chart's diagram to the XYDiagram type, to access its panes.
    XYDiagram diagram = (XYDiagram)chartControl1.Diagram;

    // Enable the X-axis zooming at the diagram's level.
    diagram.EnableAxisXZooming = true;

    // Individually enable zooming for panes.
    diagram.DefaultPane.EnableAxisXZooming = DefaultBoolean.True;
    diagram.Panes[0].EnableAxisXZooming = DefaultBoolean.False;

    // Specify how zooming is performed.
    diagram.ZoomingOptions.UseKeyboard = false;
    diagram.ZoomingOptions.UseKeyboardWithMouse = true;
    diagram.ZoomingOptions.UseMouseWheel = true;
}

Imports System.Windows.Forms
Imports DevExpress.Utils
Imports DevExpress.XtraCharts
' ...

Private Sub Form1_Load(ByVal sender As Object, _ 
ByVal e As EventArgs) Handles MyBase.Load
    ' Cast the chart's diagram to the XYDiagram type, to access its panes.
    Dim diagram As XYDiagram = CType(chartControl1.Diagram, XYDiagram)

    ' Enable the X-axis zooming at the diagram's level.
    diagram.EnableAxisXZooming = True

    ' Individually enable zooming for panes.
    diagram.DefaultPane.EnableAxisXZooming = DefaultBoolean.True
    diagram.Panes(0).EnableAxisXZooming = DefaultBoolean.False

    ' Specify how zooming is performed.
    diagram.ZoomingOptions.UseKeyboard = False
    diagram.ZoomingOptions.UseKeyboardWithMouse = True
    diagram.ZoomingOptions.UseMouseWheel = True
End Sub