par(mai=c(2,2,2,2))
plot(1:10)
legend(1,-1,"aaa",xpd=TRUE,box.lwd = 3,
       pch=15)
legend(11,11,"bbb",xpd=TRUE,box.lwd = 3,
       pch=15)

par(mai=c(2,2,2,2))
plot(1:10)
legend("topleft",inset=c(0.01,0.2),"aaa",xpd=T,box.lwd = 3,
       pch=15)