Could a jet engine be made from cast aluminium?
Short answer: No.  Unfortunately the yield strength of typical aluminum alloys drops off after about 300° F and long term exposure to high temperatures dramatically affects their creep and fatigue lives.  Typical aviation gas turbine hot sections run between 3000°-3800° F and rotate at angular speeds as high as 40,000 RPM, making Aluminum totally unsuitable for this role.  Most hot section components eg cumbustors, stator buckets, rotor buckets, etc.  are manufactured from exotic nickel-cobalt superalloys and employ novel single crystal casting techniques as well as passages to bleed compressor air as a boundary layer over them to protect them from that kind of intense heat.