Juntar 2 arrays com PHP

array_merge(array ...$arrays): array

$arr1 = [0, 1, 2, 3, 4];

$arr2 = [5, 6, 7, 8, 9];

array_merge($arr1, $arr2); // [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]