lineThickness : Number

Sets the Thickness of Axis line in pixels.

Default: 2
Example: 5, 8..

var  chart =  new  CanvasJS.Chart("container",
   lineThickness: 3,

Try it Yourself by Editing the Code below.

  Also See:    

In order to provide better support, we have closed the comments and switched completely to our Forums.
If you have any questions, please feel free to ask in our forums.