Safety base alloy crack

I have a Strida 3.2. The base that holds the safety lever has been cracked. I tried to repair it in an alloy workshop by it keeps cracking. The people there told me to find that precise alloy type so they can mould the correct one. Does anyone know which aluminum alloy was used in the 3 series?

Alternatively do you know whether I could replace the whole front part minus the folding handlebar?

[url]Old stuff about the past generations of Strida]
Frame Material:
Strida 1, 2 & 2.5: 5251 Aluminium Alloy
Strida 3, 5 & Mini: 7005 T6 Aluminium Alloy