Merge two data.frames with replacement

I have two datasets. First one is smaller, but have more precise data. I need to join them, but: 1. If I have some data in Data1 - I'm using only this data. 2. If I haven't got data in Data1, but they're in Data2 - I'm using only data from Data2.

Data1 <- data.frame(
    X = c(1,4,7,10,13,16),
    Y = c("a", "b", "c", "d", "e", "f")
)

Data2 <- data.frame(
    X = c(1:10),
    Y = c("a", "b", "c", "d", "e", "f", "g", "h", "i", "j")
)

So my data.frame should look like that:

DataJoin <- data.frame(
    X = c(1,4,7,10,13,16,7,8,9,10),
    Y = c("a", "b", "c", "d", "e", "f", "g", "h", "i", "j")
)

How can I do that? I've tried somehow option merge form base package and data.table package, but I couldn't make it happend, as I like.