Magnesium alloy and dug of figuration of welding line of steel agitate friction welding

Summary: The article soldered with method of agitate friction welding heterogeneous material magnesium alloy and mild steel, analysed the sectional form appearance of contact and hardness. The result makes clear, should solder when craft parameter is appropriate, can win the butt joint contact of the magnesium alloy with exterior good, flawless figuration and steel. To contact, metallographic analysis makes clear, in welding line cross section, broken steel bead and magnesium alloy assume better mixture position, inside the plane of surface of parallel welding line, broken steel bead distributings into insular shape within magnesium alloy. Hardness experiment makes clear, local district is had inside solder nucleus taller microscopical hardness, the generation of local district tall hardness likelihood and in solder nucleus bead of local district presence is large steel is concerned. Introductive magnesium alloy is current one of the lightest metallic construction material, have taller than intensity, than stiffness [1, 2] , be known as material of project of 21 centuries green [3] , be applied extensively at the domain such as car, shipping, aerospace. Steel is the black metal with the at present widest application in industry. Current, the join technology between the nonferrous metal such as alloy of steel and aluminium alloy, copper alloy, titanium has matured with each passing day, but the join of steel and magnesium alloy returns the primary level at research. Domestic magnesium and steel solder basically is fusion welding at present, if place electric arc of nickel layer laser compound solder [4] , but magnesium and difference of steel melting point type of big, crystal lattice is different, cause them to issue dissolve of extremely difficult each other in liquid state thereby [5] , solder with fusion welding method so magnesium and steel are more difficult, and the cost that laser beam welding receives is higher. If can realize the high grade join of magnesium alloy and steel, will reduce automobile body weight for auto industry implementation is energy-saving the method that decreases a platoon to offer a kind of effective. Accordingly, the join problem of magnesium and steel already got the attention of domestic and international broad scholar. Agitate friction welding (Friction Stir Welding, FSW) , it is method of a kind of new solid state join. Current, the research of agitate friction welding that domestic and international scholar waits for a metal to aluminium alloy, copper and its alloy is more, research shows agitate friction welding can rise solder the mechanical function of contact, avoid the flaw that appears when fused solder, and contact heat affects an area microstructure change is minor [6] . In view of agitate friction welding a series of advantage, the join that the agitate head of bougie of cylinder of face of foreign scholar consumed realized magnesium alloy and steel successfully [7] , but solder contact effect of compound of two kinds of material is not very ideal. The article is research target with magnesium alloy and steel, use the agitate head that carries whorl bougie to have a test, solder to magnesium and steel solid state analysis of welding line figuration, provide experimental basis to solve the join technology of magnesium and steel, lay a foundation for the following thorough research at the same time. 1 test data and method 1.

The data that experiment of 1 test data uses is out of shape for AZ31B magnesium alloy, ply is 4mm and Q235 mild steel, ply has butt joint test for 5mm, if its chemistry composition is expressed 1 with the watch 2 are shown. 1.

Test of 2 experiments means uses a butt joint, agitate head is made with high temperature alloy, diameter of shoulder of agitate head axis is 24mm, take whorl bougie diameter 5.

4mm, bougie is long for 3.

5mm, the agitate friction welding that changes his costume or dress in milling machine with self-restrained fixture undertakes soldering experimenting on machine. Solder chosen experimental parameter solders speed 47.

5mm/min, agitate head rotate speed coming back spends 950r/min, bougie deflection is measured 0.

15mm, the amount is controlled below axial shoulder 0.

3mm and 0.

4mm, head of the agitate in experimental process rotates dip angle is 2 ° . In the experiment, the volume that bougie deflection measures with magnesium alloy of bougie center deflection when, bougie external diameter and magnesium / the distance of armor plate juncture will decide. The two kinds of metals butt joint face before solder and fluctuation surface use light of sand paper burnish, swab with acetone next, after purify is smeary, to soldering with avoiding the oxide of workpiece surface quality produces adverse effect. When soldering, adjust agitate head to rotate above all the deflection quantity of dip angle and bougie, choose to solder suitably next craft parameter undertakes agitate friction welding experiments. After solder, observe figuration of welding line surface and preparation metallographic sample, the analysis solders the sectional form appearance of contact; Show with MVD-401 number microscopical sclerometer, cross section of edge welding line undertakes microscopical hardness checks. 2 tests result and analysis 2.

The exterior figuration of 1 magnesium alloy and steel FSW connect pursues 1 in (A) , (B) to solder head of speed, agitate rotates when speed and deflection amount are same, the quantity is pressed to be respectively below 0.

3mm and 0.

The appearance of exterior figuration form of the butt joint connect that gets when 4mm pursues. See by graph 1a, instantly pressing quantity is 0.

When 3mm, the exterior figuration of welding line is good, magnesium of exterior existence minority is oxidized, but wait for blemish without groove and crackle. Graph 1b is measured to next pressing for 0.

The figuration of welding line surface when 4mm, visible welding line oxidizes badly, occurrence crackle of spoon opening position, mild steel and magnesium alloy cannot form good union. When heterogeneous metal solders, change function to differ as a result of the content of two kinds of material too big, the quantity of heat that place of attrition of the agitate below next similar action that control an amount produces is right the action result of two kinds of metals is different also. Soldering suitably the quantity of heat that place of attrition of the agitate below parameter produces can make magnesium achieves very good model to change position, the broken steel bead in agitate process and magnesium alloy are contacted adequately, the physics between implementation atom is united in wedlock and obtain solder flawlessly contact. Magnesium alloy coefficient of thermal conductivity is tall, melting point is low, be less than the 1/2 of steel melting point, solder parameter chooses unreasonable agitate attrition heat is exorbitant, soldering the quantity of heat in the process is conducted to magnesian side quickly, temperature crosses Gao Mei easy combustion and affect welding line figuration. Additional, the hot coefficient of expansion of magnesium alloy is big, it is 2 times of steel about, stretch model volume is minor, soldering the cooling rate in the process is mixed quickly solder the tigidity of contact is cabined degree bigger, easy cause greater internal stress, make weldment easy generation larger thereby solder be out of shape. Graph 1b solders next the process is medium pressing the amount is too large, agitate attrition heat is exorbitant bring about afore-mentioned occurrence of all sorts of circumstances and make welding line appears crackle. 2.

The sectional form appearance of 2 magnesium alloy and steel FSW connect pursues the 2 sectional configuration that are magnesium alloy and welding line of connect of steel butt joint, welding line is left for steel, magnesium alloy is on the right side of. From the steel bead that can discover existence of magnesium alloy side is petty in the graph, mix with the metal of agitate area formed solder nucleus. In steel side, the dividing line of solder nucleus and mother capable person is clear, bulky steel particle size distribution is in in the interface; And in magnesium alloy side, dividing line is inferior to former and apparent, and distributing to handle steel pellet in the interface relatively fine; Welding line center also appears the iron grain with larger minority. Solder nucleus area is two kinds of mixture organizations that metallic stuff forms. Nextpage pursues 3b of 3a of sectional configuration plan, graph mixes 2 connect graph 3c is a graph 2 in A, B, C the enlarge graph 3 o'clock. Graph 3a is visible, the graph is left area of capable person of the mother that it is steel, welding line area is on the right side of, cut margin of matrix of distributinging Yu Gang of zonal metal strip; Graph 3b is welding line mid, steel grain is less and grain is relatively fine in matrix of distributinging Yu Mei of the shape that show an island; In graph 3c on the right side of to be close to matrix magnesium, left area of bed welding line brim, the steel bead of tiny island shape distributings in magnesium alloy, and the steel grain that nears area of welding line of matrix magnesium alloy more is finer. The steel of interfacial part is below be heated and mechanical integrated action, break away from with matrix, rotate in agitate needle below action, enter magnesium alloy a side. Stand by interfacial steel, basically accept agitate pin cut action, reservation comes off from steel matrix the condition that come down, appear to cut a ribbon bulkily, and be far from solder nucleus cut metal strip to be in the agitate of agitate needle, attrition is mashed below integrated action, in magnesian matrix the shape that show an island distributings. Temperature of process of agitate friction welding is relatively inferior, steel has not achieved model completely to change condition, magnesium had achieved good model to change condition, the plasticity flow of magnesium alloy is right now better. Get petty steel bead follows magnesium alloy one case below bougie mix effect plasticity is migratory reach the magnesium alloy side that is far from an interface to welding line center, bulky steel bead plasticity sheds moment, follow magnesium alloy one case hard Sunday run undertakes migratory, be gone to by agitate keep long in stock gradually in plasticity flow process of the metal near welding line brim. 2.

3 solder contact hardness pursues 4 what go up for contact cross section is microscopical hardness profile graph. By hardness profile the graph can be discovered, the hardness of Q235 mild steel is controlled in 170HV, steel side stands by the hardness of steel of solder nucleus area to increase to be concerned with the fine brilliant aggrandizement of this area. Graph 5 it is a graph 4 in steel side stands by an interface local hardness is taller area is sectional form appearance graph, this area wants than the average hardness of base material steel tall, because this area is in,this is heat up and acuteness plasticity arose to be out of shape below the action with the integrated extruding of axial shoulder and bougie, grain gets refine and be changinged equably, microscopical hardness refine and increase as grain, this also accords with Huo Er one admire strange formula. The average hardness of AZ31B magnesium alloy is controlled in 62HV, the highest hardness value of solder nucleus area achieves 180HV, greatly prep above magnesium alloy the hardness of mother capable person, value of hardness of solder nucleus area distributings inhomogenous because size of bead of the place steel becomes insular shape differly to distributing,be in magnesium alloy. The generation of local district tall hardness may be in solder nucleus place of bead of local district presence is large steel comes. Graph 4 graphs the 5 sectional form appearance that stand by interfacial steel 3 last words 3.

1 should solder craft parameter choice is right, with method of agitate friction welding the connect of the magnesium alloy with good, flawless figuration of surface of attainable welding line and steel. 3.

2 approach interfacial point, the existence in solder nucleus cuts metal strip bulkily, be far from an interface, the steel bead in solder nucleus is pettier. 3.

The 3 effects that suffer fine brilliant aggrandizement stand by the hardness of interfacial steel to increase, the steel bead that shape of the island in solder nucleus distributings causes hardness profile inhomogenous, local hardness is bigger. CNC Milling