php如何实现两个数组合并

php怎么实现两个数组合并
数组一：
$a_array = Array
(
[0] => Array
(
[plan_id] => 1
[ad_img_url] => http://www.adsload.com/assets/ad1.jpg
)

[1] => Array
(
[plan_id] => 2
[ad_img_url] => http://www.adsload.com/assets/ad2.jpg
)

[2] => Array
(
[plan_id] => 3
[ad_img_url] => http://www.adsload.com/assets/ad3.jpg
)

)
数组二：
$b_array = Array
(
[0] => Array
(
[plan_id] => 1
[ad_url] => http://www.baidu.com/
)

[1] => Array
(
[plan_id] => 2
[ad_url] => http://www.baidu.com/
)

[2] => Array
(
[plan_id] => 3
[ad_url] => http://www.baidu.com/
)

)
合并后：
$ressult_array = Array
(
[0] => Array
(
[plan_id] => 1
[ad_img_url] => http://www.adsload.com/assets/ad1.jpg
[ad_url] => http://www.baidu.com/
)

[1] => Array
(
[plan_id] => 2
[ad_img_url] => http://www.adsload.com/assets/ad2.jpg
[ad_url] => http://www.baidu.com/
)

[2] => Array
(
[plan_id] => 3
[ad_img_url] => http://www.adsload.com/assets/ad3.jpg
[ad_url] => http://www.baidu.com/