procedure TForm1.Button3Click(Sender: TObject);
var
  I,Len : Integer;
  Array1 : Array OF double;
begin
  Len := Chart1.Series[0].Count; //Depend on which series that you want get
  SetLength(Array1,Len);
  For I := 0 to Len - 1  do
    begin
      Array1[i] := Chart1.SeriesList.Series[0].XValue[i];
    end;
end;