This invention discloses a method for manufacturing a precision-cast aluminum
alloy underbeam welded component for an off-road
vehicle frame. The method includes: preparing an Al-Si-Mg-Mn-Zr-Ti-Sr-B series cast aluminum
alloy; melting, degassing, and filtering the aluminum
alloy material, followed by modification and grain refinement treatment; forming the underbeam
casting blank using
precision casting, and setting local feeding and / or local cooling in the
welding connection area to form a refined and dense structure with a secondary
dendrite spacing of no more than 35μm in the
welding connection area and within 20mm to 50mm on both sides; performing
solution treatment,
quenching, and under-aging pre-weld heat treatment on the
casting blank; performing final
surface cleaning of the
welding connection area before welding, and welding the underbeam
casting blank to a crossbeam, reinforcement, connecting seat, mounting lug, or another underbeam segment using low heat input welding within 4 hours after cleaning; and finally performing post-weld graded
artificial aging treatment. This invention improves the problems of heat-affected zone
softening, weld mismatch between weld and base material properties, and
fatigue cracking induced by casting defects in welded aluminum alloy
vehicle frame bottom beams by coordinating material composition, casting structure, welding heat input, and post-weld structure
recovery. It is applicable to off-road
vehicle frame bottom beams and other aluminum alloy cast-welded composite load-bearing structural components.