Why this source code giving output "system.int32[]" instead of values of merged array.please suggest

using System;
using System.Collections.Generic;


namespace ConsoleApplication2
{
    class Program
    {
        static void Main(string[] args)
        {
            Program dn = new Program();

            int[] array1 = { 1, 2, 3 };
            int[] array2 = { 1, 2, 3 };
            int[] res = dn.merge(array1, array2);

            Console.WriteLine(res);
        }

        public int[] merge(int[] array1, int[] array2)
        {
            int[] array3 = new int[6];
            int[] arr4 = new int[6];
            int i, j;
            int array1length = array1.Length;
            int array2length = array2.Length;
            //array3 = array1.Concat(array2).ToArray();
            for (i = 0; i < array1length; i++)
            {
                array3[i] = array1[i];
            }

            int FinalLength = array1length + array2length;
            for (j = 0; j < array2length; j++)
            {
                i++;
                array3[(i - 1)] = array2[j];

            }
            for (int k = 0; k <= arr4.Length; k++)
            {
                arr4 = array3;
            }
            return arr4;
        }
    }
}