How to make the transition from aluminum to copper wire?

sergey asks:

Good afternoon. I ask for advice from an electrician. I have a house in SNT, the situation is as follows, now two old single-core wires with a cross section of 1X16 sq.mm are coming from the post. in the barn (as I understand it, this is the APPV wire in white single-layer insulation, it is in single-layer insulation), the task stands like this - you need to cut the same wire and connect it to the copper lead-in cable for 6 sq., already on home. The question arose - can this single-core wire (APPV) be connected to the lead-in copper wire as well as the self-supporting insulated wire, that is, through piercing contacts? Doubt has arisen because I am afraid to pierce the APPV, there may not be good contact when piercing. I also thought about the next option - to use a piercing clamp, which goes for the version of the main line without insulation, when only the copper wire is pierced, and the second part simply clamps the bare cable, in this case, you can simply squeeze the stripped one at the end APPV.

PS: There is no way to replace it with a self-supporting insulated wire, you need to use the old wire.