Effect Of Alloying Elements And Smelting Technology On Hydrogen Content&the Weld Properties Of Al-Si Wires

Aluminum alloys are extensively utilized in industry due to excellent mechanical and physical properties.Owing to the excellent fluidity and weldability,the Al-Si alloy wires are widely used for the welding of 2 series and 6 series Al alloys with high hot cracking tendency.However,at present there is a big gap in quality between domestic Al-Si alloy wires and imported ones because of many reasons.Especially in automatic welding process,the domestic Al-Si alloy wires have poor wire feeding,so Al alloy wires for high-end equipment manufacturing in China entirely depend on imported ones,which are expensive and have the problem of slow response of after-sale service.In this study,to make domestic Al-Si alloy wires reach advanced level abroad such as French SAF alloy wires,novel Al-5Si/12Si-x Sr-y Ce alloy wires were developed and used for welding 6082 Al alloy.The effect of alloy elements and smelting process on the H content of Al-Si alloy wires and the microstructures and mechanical properties of weld were investigated.Firstly,the smelting process of Al-Si alloy wires were optimized and the effect of Ti,Sr and Ce on the microstructure and mechanical properties of Al-5Si alloy wires were investigated.The results indicated that the Al-Si alloy melt with the minimum initial H content of 0.10 m L/100g Al after smelting could be obtained by using the 0.5 wt.%C₂Cl₆-containing self-made refining agent jointly with the99.99%argon with a flow rate of 10 L/min.The chemical composition results showed that only the content of Sr progressively decreased with the increase of holding time.Adding 0.08 wt.%Ti to Al-5Si alloy wires refined the?-Al dendrites obviously but was incapable of altering the needle-like morphologies of eutectic Si phases.Adding 0.025 wt.%Sr reduced the ratio length/width of needle-like eutectic Si phases but was useless for the?-Al dendrites.When 0.08 wt.%Ti and 0.025 wt.%Sr are both added,these elements can affect synergetically the microstructures of Al-5Si alloy wires.Adding 0.08 wt.%Ti and 0.03 wt.%Ce at the same time refined?-Al dendrites and improved the morphology of eutectic Si phases.If excessive Ce was added,there were considerable needle-like Fe-containing and Ce-rich intermetallic compounds(IMCs)appearing.The increase of size and volume fraction of the needle-like Fe-containing and Ce-rich IMCs reduced the ductility of Al-5Si alloy.By comparison,the modification effect of Sr on eutectic Si phase is more significant than that of Ce.Sr mostly evolved to the Al₂Si₂Sr phase during the eutectic reaction and enriched at the forefront of Si phase in the Al-5Si alloy,which accelerated the eutectic Si phase to change from lamellar or coarse needle-like morphology to fine granular structure.The atomic radius ratio of Ce to Si is close to 1.65,Ce will enrich on the growth step of solid-liquid interface of the Si phase,which can induce twin growth and change the morphology of eutectic Si phase.The effects of Sr and Ce addition on the microstructure and mechanical properties of Al-12Si alloy wire were investigated.The differential scanning calorimetry test indicated that the solidus and liquidus temperature of Al-12Si alloys changed little with addition of Sr and Ce.The microstructure analysis showed that with the increase of Sr content in 0-0.08 wt.%,the growth of columnar?-Al dendrites was accelerated and the size of the?-Al dendrites was refined,the primary Si phases were disappeared and the eutectic Si phases were fully modified when the content of Sr was 0.025 wt.%.The addition of Ce could also refine?-Al dendrites,eutectic Si phases and primary Si phases.When the Ce content was0.08 wt.%,?-Al dendrites were refined significantly,while the eutectic Si phases maintained a needle-like structure and the size decreased slightly.When further increasing the addition of Ce to 0.8 wt.%,the size of the eutectic Si phases was the smallest,meanwhile,large number of Ce-rich IMCs and needle-like Fe-containing IMCs were precipitated,and the size and morphology of Ce-rich IMCs were related to the mass fraction ratio of Ce to Fe.The improvement effect of Sr on the mechanical properties of?10.0 mm Al-12Si cast rod was better than that of rare earth Ce.In the range of 0-0.08 wt.%with the increase of Sr content,the yield strength of the cast rod increased linearly,tensile strength and elongation first increased and then decreased.In the range of 0-0.8 wt.%with the increase of Ce content,the quality index of the cast rod first increased and then decreased.The H content results in liquid and solid Al-Si alloy showed that the H content of unmodified Al-Si alloy decreased with the increase of Si content in the range of 0-12 wt.%.The H content in Sr-containing Al-Si alloy wires increased rapidly with the increase of Sr content.The H content in liquid and solid Al-5Si-0.08Ti-0.02Sr alloy was increased 77.27%and 105.41%respectively compared with Al-5Si-0.08Ti alloy wire,the H content in liquid and solid Al-12Si-0.03Sr alloy was increased 87.5%and 103.33%respectively compared with unmodified Al-12Si alloy wire.Rare earth Ce exhibited good“H fixation”and“H removal”effects in both the holding period and casting stage of the Ce-containing Al-Si melt.The weld percent porosity(WPP)and mechanical properties testing results of tungsten inert gas(TIG)welded joints showed that the WPP of Sr-modified alloy wires was greater than 0.5%,while that of Ce-modified alloy wires was less than 0.5%.Due to serious overaging in the heat-affected zone(HAZ)of the TIG welded joint,the tensile fracture of the TIG joints welded by Sr-modified and Ce-modified alloy wires mainly occurred in HAZ,and the tensile strength of the joints had a linear relation with the total heat input(TQ).Due to low heat input and high sensitivity to porosities of metal inert gas(MIG)welding,the WPP of the MIG joints welded by unmodified and Sr-modified Al-Si alloy wires increased compared with that of TIG joints,the tensile fracture of the MIG joints occurred in weld zone(WZ),and the elongation of the MIG joints decreased due to excess porosities.The WPP of the MIG joint welded by Ce-modified Al-Si alloy wire was relatively low,the tensile fracture occurred in HAZ.In addition,the bending test results of weld showed that the bending properties of TIG joints and MIG joints welded by Sr-modified or Ce-modified Al-Si alloy wires were not up to standard.The results of composite addition of Sr and Ce in Al-Si alloy wire showed that the H content in liquid and solid Al-5Si-0.08Ti-0.01Sr-0.03Ce alloy were decreased by 30.8%and 38.5%respectively compared with Al-5Si-0.08Ti-0.01Sr alloy wire,while the H content in liquid and solid Al-5Si-0.08Ti-0.02Sr-0.03Ce alloy both exceeded the limits.The H content evolution of Al-12Si alloy wire with the composite addition of trace Sr and Ce is similar with that of Sr-Ce modified Al-5Si-0.08Ti alloy wire.The composite addition of Sr and Ce in Al-5Si/12Si alloy wires led to the fully modification of eutectic Si phases,and crack was likely to be first initiated and rapidly propagated in the region where coarse needle-like Fe-containing or Ce-rich IMCs existed.The tensile strength of?10.0 mm Al-5Si-0.08Ti-x Sr-0.03Ce cast rod was lower and the elongation was higher compared with Al-12Si-y Sr-0.08Ce cast rod.Only welded by Al-5Si-0.08Ti-0.01Sr-0.03Ce and Al-12Si-0.015Sr-0.08Ce alloy wire,the WPP of MIG joints were qualified,the tensile fractures occurred in HAZ,and the tensile strengths were nearly the same.The bending property of the MIG joint welded by Al-5Si-0.08Ti-0.01Sr-0.03Ce alloy wire was qualified,while the bending fracture angle of the Al-12Si-0.015Sr-0.08Ce alloy wire increased by nearly one time compared with the that of unmodified Al-12Si alloy wire.Moreover,the structure and principle of a novel apparatus,which can enhance the feedability of the Al-Si alloy wire,are introduced and the apparatus can achieve the rough and fine adjustments of cast and helix of the alloy wire.