Pulse laser solders research of feasibility of aluminium alloy mould

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The laser beam welding of introductive aluminium alloy is received is in recent years the most popular research project. Many units studied a lot of laser beam welding receive the technique of aluminium alloy. Laser beam welding receives be research and development of nearly 20 years of ability to make new technology, making current treatment tool, be sure to replace traditional production technique, got the height of each country government and enterprise takes seriously. A lot of good point that laser beam welding receives solders for aluminium alloy offerred a condition. The biggest characteristic that laser beam welding receives is can go to focusing of beam of light inside very little scope, and very can convenient transportation reachs the place of any need. The main good point that ◆ laser beam welding receives 1) energy density is high, hot input quantity is little, workpiece hot deflection is small; 2) fused area, hot influence area is narrow, and frit is deep very big; 3) natural cooling rate is extremely high after solder, can amount to 106 ℃ / S, solder thereby fused area organization is very subtle, make contact performance good; 4) laser does not solder together commonly, do not need electrode, reduced cost consequently; 5) laser solders unlike electron beam, do not need vacuum, improved work efficiency. What use protective gas pressure, discharge is adjustable; By solder workpiece appearance, size unlimited; 6) laser but remote carry, craft adaptability is good; 7) laser and computer, manipulator cooperate, very easy implementation solders process automation, rose to solder greatly efficiency; 8) YAG laser beam welding receives aluminium alloy, the efficiency that laser is absorbed is tall, it is about 20% . Exceed the absorptivity of pair of CO2 laser far. Because have the above-listed,the difficulty laser beam welding that ◆ laser beam welding receives aluminium alloy is received a lot of advantage, apply at all sorts of material widely solder, and application soldered to encounter a series of difficulty however at aluminium alloy, investigator noticed following laser beam welding receives the difficult point of aluminium alloy adequately: 1) aluminous melting point is low, very easy ionization falls in action of beam of light, air mass of plasma of upper part of the bath when soldering is greater, when soldering, must give break up, affect laser to absorb efficiency otherwise; 2) when aluminium alloy solders, because the element inside bath is inhomogenous,volatilize, cause solder contact bate, intensity drops; 3) the oxidation film that aluminium alloy surface puts in difficult frit (2060 ℃ of Al2O3 melting point) , the laser ability of high-power density is only fused; 4) aluminium alloy solders welding line produces air hole easily, the account that produces air hole has 3: ① is deliquescent the hydrogen in bath (aluminium sucks hydrogen easily in liquid state) did not spill over again in the separate out in cooling process dissolve pool, form air hole, call metallurgy air hole; The water in the oxidation film with ② completely fused unfinished divides hydrogen of pyrolysis separate out, film of oxidation of its leech on to and form air hole, call oxidation film opening; Aperture of the spoon when ③ deep fusion welding is not stable, stay not the aperture of cram, call solder root hole; 5) cooling rate of aluminium alloy welding line is quite rapid, can amount to 106 ℃ / S, when bath is caky columnar brilliant development is splitting, extremely any crystalline substance of Yi Zaizhu form is sectional generation crackle, call crystallization crackle; Because refrigeration contracts to also be met,crackle is formed around welding line, call liquefacient crackle. Generally speaking the possibility that alloying element content produces crackle higher is larger, solder number of the crackle in rate is older welding line is more; 6) the coefficient of expansion of aluminium alloy is big, make weldment is out of shape extremely easily in cooling process; 7) the heat conduction rate of aluminium alloy is old, it is 4 times of steel about, use model solder to need higher power density. Experiment method and laser of pulse of YAG of craft choice ◆ solder equipment my company was introduced by company of German Luo Fen 2006 " Ⅱ of SW TOOL OPEN " machine of laser beam machining, its are main index is as follows: (1) laser type: Nd:YAG (2) laser wavelengh: 1.

6um (3) pulse width: 0.

3 ～ 20ms (4) pulse frequency: 1 ～ 20Hz (5) energy of the biggest pulse: 100J (6) the greatest average power: 150W (7) power of pulse of the greatest peak value: 10kW (8) facula diameter: 200 ～ 1200um (9) horn of diverge of beam of light: 235mrad (10) mode: Much model ◆ considers to because the alloying element content of 2A12 aluminium alloy is higher,use aluminium alloy data, solder hind appears extremely easily crackle and intensity drop. Be based on aluminium alloy stronger to laser reflectance, need of surface of 2A12 aluminium alloy is black change processing, in order to increase the absorption of 2A12 aluminium alloy to laser. The experiment adopts the 2A12 aluminium alloy that the surface does not handle first, if not OK, introduce a course again the surface is black the 2A12 aluminium alloy that turns processing. The choice of ◆ protection gas introduces according to the data, aluminium alloy laser beam welding receives protective gas to had better use He-Ar gas mixture, protective gas velocity of flow is 10L/minHe+5L/minAr about. Protective gas needs to have enough purity, ask H2 and H2O content want especially low. Aluminium absorbs hydrogen extremely easily in liquid state, and in the separate out in cooling process, form air hole; With AL happening reaction gives off H2 below H2O high temperature, also can form air hole. Hydrogen is very good protection gas, but the more than heat that solders to be taken away not only to the laser of aluminium alloy is little, and the plasma air mass of bath upper part is serious, because this uses pure argon,making protective gas is not very advantageous. Nevertheless, consider at present the condition is reached solder cost, study originally or choose pure argon Ar to make protective gas. The craft parameter that when YAG pulse laser solders, the choice of parameter of technology of laser of ◆ YAG pulse can offer an alternative has: D of diameter of F of frequency of T of width of pulse energy J, pulse, pulse, facula. According to data introduction, pulse laser solders to use deep fusion welding rarely, although can deep fusion welding, use commonly conduct solder, and aluminium alloy conducts solder power density to be 105 ～ 106W/cm2, that is to say density of the power when aluminium alloy solders cannot choose too tall. The welder of YAG pulse laser that we choose, t of width of pulse energy J, pulse has place issueing a list to list a concern, and pulse energy J decided pulse frequency F again. Should choose bigger pulse energy, because coefficient of aluminium alloy thermal conductivity is bigger, it is 4 times of steel; The oxidation film that aluminium alloy surface has difficult frit again (Al2O3) ; Aluminium alloy is reflexed to laser serious. Quality inspection of welding line of ◆ aluminium alloy to define quality of aluminium alloy welding line, undertake the exterior examines above all, for example: Is figuration of ① welding line good? Whether to have splatter? Whether does welding line join? Whether to have flaw? Should stay when necessary have exterior photo; Cross section of ② welding line organizes a state, frit area appearance, stomatic, crackle, organization, stay when necessary take microstructure photo; Appearance of ③ welding line concerns dimension, welding line frit is deep, welding line width, half deep width. Function of welding line of ◆ aluminium alloy detects whether to exist to beg card aluminium alloy to solder composition is inhomogenous volatilize, need to use electronic probe to soldering each element content undertakes the aluminium alloy material of around be analysed completely, basically measure content of Cu, Mg. Meet via soldering to beg card aluminium alloy bate, thereby intensity drops, need those who do tensile strength Ob to determine. The frit that experimental result measures on solder road cross section is deep with pulse energy relation result is shown at the graph 1, from the graph 1 in reach this equipment solders the biggest frit can amount to 2A12 aluminium alloy greatly 0.

33mm. Experiment place solders crackle of crystallization of path of 2A12 aluminium alloy solder is serious, stomatic more, if pursue,2 are shown. CNC Milling