These two words are similar but they still have difference. In most cases, they are replaceable. But Chinese people will say 十二生肖, we never say 十二属相. We accustomed to use 属相 when we ask or introduce our zodiac sign. When we say the 12 animal sign of the Chinese horoscope, we always say 生肖. example: －你的属相是什么？ －我的属相是牛 / 我属牛 －牛在中国的生肖里 / 中国的十二生肖里有牛

They have the same meaning and usage.But 生肖 is more frequently used in Chinese people‘s daily life.You can say ‘我的生肖／属相是...’or‘我属...'.

and I think 生肖 contains more meaning. It means also the collectively of 12 animals. But 属相 is a narrower definition. Orally we say 我的属相是 or 我属...生肖as I think is just a collectively.

same in using and meaning

Same uses, “你属(no 相)什么的？"is commonly used, the answer will be “我属……(鼠牛虎兔龙蛇马羊猴鸡狗猪)” Usually can guess someone's age by asking the question