I want to use this automotive relay to switch 60VAC, the current max. is 10A. But all its parameters are for DC usage. Can I use it safely to switch AC? It states its "Max. switching voltage" is 50VDC, then what about AC? How can I infer the AC parameters?
Given that AC voltage is usually measured in RMS, that means the peak voltage you expect to see on your AC line is 60 * sqrt(2) ~= 84.85 V(peak). This is quite a bit higher than the rated 50V(dc) (peak is the same as given voltage for DC), and you could possibly damage the device and the rest of your circuit.
EDIT: I had a another look at the data sheet, and the issue you may run into is that if you select one of the options with a diode (called a freewheel diode, used to prevent reverse voltage spikes when the contacts are opened), it will cause issues as the diode will conduct when the AC voltage goes negative (even with the contacts open).
Also, I'm assuming you are using a DC control current with a AC load current
I've used them in a pinch in lighting scenarios and never had trouble. Lasted longer than my solid state relay for a tiny fraction of the price. It's the size of the load I worry about. I've never went over than a few amps.