try this
var selectedRowChartID = ['a', 'b'];
var obj = JSON.stringify({ chartIDList: selectedRowChartID });
$.ajax({
type: 'post',
url: '@Url.Action("SaveAuditTrail", "DMS")',
contentType: 'application/json; charset=utf-8',
async: false,
cache: false,
data: obj,
success: function (data) { },
error: function () { alert(selectedRowChartID); }
});