CA1198039A - Process of manufacturing of aluminium wire rods - Google Patents

Abstract

ABSTRACT:

A process of manufacturing wire rods of precipitation hardenable aluminium. The first step of the process comprises an exclusively thermic step of continuously quenching a continuous bar for obtaining a restored and supersaturated structure. The second step immediately follows the first step in a same continuous operation and comprises the working, preferably rolling, of the bar at aging temperature into wire rods, which are subsequently sub-mitted to aging.

Description

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PROCESS OF M~N~F~CTU~ING OF ~LU~1H1U~ WIRE RODS

~ he inYention relates to a prooes~ Or manufacturing of wire rod~ of precipitation hardanable aluminiumO ~hi~ proce~s i~
in particular applicable to alu~iniu~ for electrieal conductor wire, i~e~ aluminiu~ that oan be trcated to wire with a resi~ti~ity of ~aximum 32 9~ milliohm~ x mm2/~, although not limited to that type o~ alumini.u~ which co~pri~eB~ a~ alloyi~g element for preci-pltation~ 0.3 to 0.9 ~ of ~agnesium9 ~.25 to 0.75 ~ of Silicon and O to 0060 % of iron7 the balance be~ng alumlnium and impuritie~
(i.e. elements in a q~a~tity of la8~ than 0~05 %) 9 parcentagec by ~eight~ Wire rods are, a~ well knOWI19 the starting product for ~ub~e~
quent drawing or rollin~, in whiGh ths cro~ action of the aluminium wire i~ reduced. The wi~e rod~ ha~e in genaral a diameter of 5 to 20 millimeter9 in most cases between 7 and 12 t~;11; eter, and a tensile strength oonsidftrably le38 than the ten~ile ~trengt~ of the fi~al product obtained by drawing, for instance, for the abo~eme~-tioned aluminium for electrical ¢onductor wire, a ten~ile ~trength of latt~ than 250 ~ewton/mm2, 3t a~y rate le~ than 300 ~/~m~. ~8 : well known; a~ter drawing, the wire i~ submitted to ~n aglng opera~
tion, in which precipitate~ are ~ormed Or the alloying eleme~ts whi¢h ~till had remained in solutio~, and thi.s agi.ng oper~tion improvas the mechanical and eleotrical ohar~cteristic0 of the wire.

The oon~entional production process of aluminium wire rods comprise~ a fir~t stap of hot rolling, in which coil~ of wire rod~
are formed, followed b~ a di~contLnuoue ~olutio~ treatment, and quenching of the coil~ obtained by hot rolling. Otherwi~te ind3ed, when the co.Ll~l are ~imply cooled down after rolling, the alloyin~
elements oome to preclpitate with the result that there are no ~lloying elemer~t~ in solution ~ny more for the ~ub~eque~t aging~

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~ ~935~ 2i ~his i~ the rea~on why these element~ are brought in ~olution again after rolling~ ~nd ars forced to remain in ~upersaturated aolution after tha imm~diately sub~equent quanching opsration.

Thi~ solution treatme~nt i~ expen~i~e ~ith re~pect to heating~ensrgy~ and moreo~er r~qu~re~ that the manufacturing bc conducted in a di~continuous way. This ia why it has been propo~ad be~ore to ~nd the ~aid fir~t step of hot rolling at a te~perature as high as pousible, in order to keep a r~imllr amou~t of alloying element~ .in ~olution9 and to quench tha wire rods9 immediately and 10 in a continuou~ process dcwnstream th~ e~it of the rolling-mill, to a quenching tem~erature~ ~n suoh a way as to keep these alloyin~
elements in ~uper~aturated ~olutionO

~ t ~uch quenc~ing temperature, the mobility of the atoms i~ S0 10~9 that the metallographic structure gets practlcally stuck in the state au it is (apart of a~ing phenomana) ~ the allogi~g ~le-ments which have .remained in ~upersaturated solution will ~o remai~
and the praclpitate~ and dislocations do not ohange. For a gi~en alloy9 the range of "quanching temperatures~ has con~equently an upper limit which is not a striot and ab~olut~ limitO Thi0 upper limit i~ deter~lned by a sufficient immobility ~f the atom which does not producs a subutantial cha~ge of the metallographic structura duriug a time period of the order o~ m~gnitude of a continuou~ procsss of treat~ent of aluminium~ i.e. of tho order of magnit~de of o~e minute. Th0 acceptable ~ limit ~or each typs of aIDy i~ ~uffi-ciently Xnown by the man skilled ln the art. For the aboveme~tionedaluminium for electrical oonductor wire, the ma~1 quenchlng tempe-rature c~l be put at 260C, although this limit i~ not an abaolute limit.

It ha~ also been propo3ed to u~e a fir~t hot rollin~ ~tep which end~ at a temperature ac high a~ po~ibla, in order to k~ep a m~irlm of alloying elaments in 301ution, followed by a quenching during whioh the metal i~ worked, and taking care that the metal be worked during the period in which it travsr~e~ the tamperature range ~3~
3.

between the maximum quenching temperature limit and the minimum temperature limit for hot working. Notwithstanding the fact that a quenching was conducted, it was observed that the alloying elements in solution did precipitate during this thermo-mechanical operation. The quantity of alloying elements kept in solution for the subsequent aging step showed to be much less than desirable, and this seemed to be a drawback. But it was observed that the so obtained wire rods were of that sort that, according as the precipitation had been partial or total, the necessity of aging after subsequent drawing was eliminated, either partially or totally. Conseqently, the expected drawback did not exist, and wire rods were obtained with properties which allowed to meet more easily the prescribed require-ments for the mechanical and electrical characteristics of the wire drawn from such wire rods. Moreover, the expensive step of solution treatment was avoided, and a continuous process was obtained.

It is an object of the present invention to provide an al~ernative for this latter process, procuring the same advantages, and giving in this way an additional degree of freedom in the choice of the parameters of the process for obtaining the desired combinations of tensile strength, ductility and conductability.

According to the invention there is provided a process of manufacturing of wire rods of precipitation hardenable aluminium, the process comprising a first exclusively thermic step in which a continuous bar of said aluminium is quenched in a continuous process down to a quenching temperature whereby a restored structure is obtained with the alloying elements in supersaturated solution, characterized by a second step, thermo-mechanical and downstream the first one in a same continuous operation, in which said bar is worked at an aging temperature, .. .

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3a.

and by the fact that the so obtained wire rods are subsequently, before any subsequent working, submitted to an aging operation.

The process according to the invention, at least in preferred forms, thus comprises a first exclusively thermic step (this means : not with simultaneous working operation) in which a continuous bar of said aluminium (which, for instance, leaves a rolling~mill and in a partially cooled-down statel or which leaves a continuous casting wheel or an ëxtrusion press is quenched in a continuous process down to a quenching temperature, as determined hereabove, whereby a restored structure is obtained with the alloying elements in supersaturated solution. By "restored structure" is meant a metallo-graphic structure in which the grains, elongated by the working step, have reorganized under in1uence of heat into a more or less isotropic structure, which is the structure obtained after hot working. A minimum amount of alloying elements in supersaturation is also necessary, Eor instance at least 30% of the precipitatable elements at the temperature of solution treatment. The quenching is consequently sufficiently rapid and starts from a sufficiently high temperature to reach that goal~

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The proce~ ac~ording to the invention i~ how~ver charac-terized by a Recond ~tep~ thermo-mechanical and downstream the flr~t one in a sam~ continuous operation, ln which aaid bar i~ worked at an aging temperatura 9 and by the fact that the RO obtai~ed wire rod~
are ~ubsequently, before any subsequen-t wor~ing, ~ubmitted to an aging oper~tion~

An "aging te~pesature" i~ a temperature in~ide a temperature range of which the maximum li~i.t i~ equal to the ~ quenching tempexature limit, a~ determined hareinabove, and of which the min;r~
limit i~ determined hereunder. An aging temperature is consequently a temperature At which the ato~ are immobilized~ apart from aging phenomena which occur in a time period, longer than the duration of a continuous procss~9 i.e. of the order of magnitude of one m$nute. ~o~
e~er, when the structure i~ submitted to working at aging temperature, it has been observed that the precipitation of the alloying elements during ~uch wor~ing and during a ~ub~equent agi~g procure~ a metallo-graphic structure~ which , a~ter cold working ln-to wire9 ~how~ a very good wire quality and which ~liminate~? partially or in totality9 accordi~g as there ara still alloying elements left i~ ~upersaturatod 20 ~olution, the neoe~sity of aging after wire drawing. Such working at aging temperature is preferably a rolli~g which reduces the ~ro~
~ectional area.

For a given aluminium alloy~ the minimum limit o~ the aging temperature will be determined hereunderO It i8 known that an aluminium alloy of a given composition, in a n~t cold worked ~tate, but ¢om-prising alloying ~lement~ in supersaturated condition by ~olution treatment and quenching down to a quenching temperature, when ~uch alumini~m alloy is submitted to aging, will firstly show A ris~ of ten~ile ~trength towards A m~imnm value~ and then show a fall of it~
tensil~ strength. This is dus to the fact that the alloying elem~nts precipitate during aging whil~t the already existing precipitates further oonglomerate. The first eff~ct, which makes the tensile ~trsngth to increase9 initially dominate~, whilst the second effect, which maks~ the tensile strsngth to fall, dominate~ at the end. The minimum limit fo:r the aging temperature, for a giYen aluminium alloy ~ ~ 8 ~ ~ 5-wi-th a glven q-uantity of alloying element~ in super~aturated solu-tion, i~ the temperature in which this alu~inium, in non cold worked ~tate9 reache~ its ~Yiml~m ten~ile ~trength after three da~s (~he oold worked ~tructure reaches it~ m earlier, due to the ~oftening of the cold ~orked ~tr~oture~. For the abo~ementioned aluminium for elec~
trical conductor wire, this m;n;mllm limit iB about 130C.

~ n i~portant point in the process i~, that the second atep ia conducted immediately after the quenching operation of the fir~t step ~in ordar not to allow any changement of the structure ~hen the intermediate product i8 left without txeatment for a certain time)~
and consequently in a same continuou~ operation with the fir~t ~tep.
To that end a it i preferred to conduct the quenching o the first ~tep down to an aging temperature9 a~ determined above, 80 that the 3econd step can be started without any intermediate heating~

The aging operation following ~aid working step at aging temperature can be conducted directly at the exit of the instrument which execute~ such working, for inst~ce by free cooling to the ambient air of the wire rods, and this provokes a precipitation of the totality or only a part of the alloying elements still left in ~uper-saturation. It can be ~aid that ~n aging take~ place whan a con~ide-rable part, for in~tance half the amount of precipitatable elements after quenching, precipitates indeed during ~uch agi~g, It i~ howe~sr preferred to conduct a total precipitation9 in order to eliminate all nece~sity of aging after wire drawing and ~o eliminate all changement~
of prope~ti0s of the wire rod~ after their manufacturing. ~hen the temperature at the exit of the in~trument, which executes the opera-tion of working at aging temperature, come~ near to the ~;ni m limit o~ aging temperature~, it will ~ometi~e~ be neces~ary to ~low down the cooling of the wire rod~ at ~aid exit ~i.e. ~lower than the free cooling to ~the ambient air). This i~ dons by ~urrounding the wire rod~
by heat in~ulator~, for in~tance, by forming wire coil~ which are anclo~ed in ~ufficiently closed boxes for avoiding cooling-down by air convection. The wire rods can al~o be kept for a certain time period, b;y heating, at the ~aid exit temperature, or the temperature can even be raised above exit t~m~erature, in 80 much a~ a ~ub~eque~t ~ging i~ then conducted.

~L~Lffl~ 3~ 60 The continuou~ bar which is used at the ~tart of the fir~t step of the process can be a bar which leaves a hot forming in~tru-ment~ such as an extrusion pres~ or a casting wheel. Such hot forming operation will preferably compri~e a continuouE ca~ting ope~ation which deli~ers an aluminium ske:Ln which is directed towards the entry of a rolllng mill 9 and a hot rolling proce~3 by ~hich th~ crocs-sectional area of said ~k~in i~ reduced for fo~ing said bar. ~y "hot"
rolling ia meant a rolling with restoration during the operation or immediately thereaft2r, bsfore the subsequent quenching. For the abovementioned aluminium for electrical conductor wire, thi~ mean~ a rolling with exit temp~rature of more than 350C. The temperature at the entrance of the rolling~mill will preferably be a temperaturQ
which exce~d~ the solution treatment temperature, which means, for the aluminium for electrical conductor wire, a temperature highor than 470C.

'~he inYention i8 particularly applicable to the aluminium for ~lect~ical conductor wire of which the composition iB given herein-above. In a pxeferred mode, a continuouR process will be used, which compri~es, in ~equence from upstream to down~tream : ~ continuous oasting operation, the introduction of the skein that l~aves the con-tinuous ca~ting inctrum~nt and at a temperature of more than 470C
into a fir~t rollingrmill, the continuou~ rolling at a temperature of more than 350~C for forming a continuous bar, the continuous quenching of said bar at the exit of Baid first rolling mill 9 the introductio~
of caid bar that leave~ the quenching in~trument and at a temperaturo of mor~ than 130C into a second rolling-mill, the continuous rolling at a temperature of more than 130C, and the aging b~ frae cooling by the ambient air. ~he entrance temperature of the second rolling-mill i8 to be controlled 80 as to obtain an exit temperature of the rolling mill ranging from 155 to 1~5C, preferably 175C~

~n ~l-Mg-Si of the type 6201 has for in~tance bPen used ha~in~ the following composition : Mg : 0.60 7~; 5i oO55 ~;
Fe : 0.18 70; Zn : o.oo6 7~o; cu 0.004 ~o ; Mn . 0 015 ~0 ; Ti : 0.001 7%
V : 0.004 %~ An aluminium can however be used which is richer or poorer in alloying elements 9 dependin~ on the c06t that can be afforded or ~ W3~ 7-mu~^t be saved for a better or le~ ~ood quality due to the compo~
~ition. ~ut thi6 doe~ not affect the pos~ibilities for the chosen alloy to improve the quality by using the proce~ according to the inven-tion.

The alloy of the compo~ition above, after leaving a conti-nuou6 casting wheel in the for~ of a skein having a cros~-sectional area of about 2000 ~m ~ is introduced at a temperature of 490C into a first continuou~ rolling mill with 9 pas3e~. It leaves said rolling mill in the form of a round bar of a diameter of 15 mm and at a tempe-rature of 430~. At this temperature mo3t of the alloying ~lement~ are still in solution, because, in ~tate of equilibrium, only 20 % of the Magne~ium and Silicon, precipitatable in the form of Mg2Si, i~ then in precipitatad form.

This bar, which leaves said first continuou~ rolling mill at a ~peed of about 2,4 m/sec9 is then d$rected towards the entry of a second continuous rolling mill, of which the entrance i8 located at about 2 met~rs from the exit of ths fir3t one. Between both, the bar pa0ses through a tubs of 30 mm diameter and 1 mater length~ which iP ~upplied by a refrigerating emul~ion in counter~current, of which the throughpUt i~ controlled in such a way that the bar leaves the tube at a tempexatur0 of 220C. Other ways of quenGhing can also b0 u~ed, for instance by ~quirts of emulsion directed towards th0 bar, in 80 much a~ the temperature can be controlled at the desired tempe rature.

The c2cond continuou~ rolling mill compri~es four pa~e~
with equal cro~s-~ectional reduction, which reduces the bar into ~rire rods of 915 mm d~ameter, which leave ~aid second rolling mill at a temperature of 175C and at B ~peed Or about 6 meter per ~e¢ond. The wire roda are cubsequently coiled up and the coil is placed in a container made of refractory brick. The import~lt point is, that the containar b~ closed 80 that cooling~dow~ by free air convection ~round the coil be avoided. ln the case of the example, the cooling down had a rate of 2~ per hour.

d3~ 80 The obtained propertie~ can now be compared with the pro-pertie~ obtained with wire rods of the same composition7 made by the conventional method which is : continuou~ casting followed by a con-tinuou~ hot rolling9 coiling-up into coils which freely cool down in the ambient air9 subsequently a solution treatment in which the coil~ are kept in a furnace during 8 hour~ at a temperature of 550C t and then quenching the coilæ do~n to a temperature of about 45C.

~hese two types of wi:re rods of a diameter of 9,5 mm~ the one according to the in~ention 7 the oth~r one aocording to the conven lQ tional method are then drawn into wire, down to 3~60 mm diameter and then further to 3,15 mm. The drawn wire obtained by the con~antional method iB then subs~quently submitted to an aging operation during 5 hour~ at 160C.

The comparative re~ults are as follows :
~-5 According toConventional in~ention method R ~ ~ R ~ p Wire rods 304 7-75 31.10 196 21 Ater drawing to 3,60 mm 348 5 31.30 285 4.5 34-9 After drawing to 3,60 mm + aging - - ~43 7.532-13 After drawing to 3,15 mm362 4~5 31-44 2go 4 34-70 After drawing to 3,15 mm ~ aging - - - 350 7 31-95 R ~ ten~ile ~trength in ~ewton/mm2 ~ ~ ductility (~o) P - re~istivity (m~mm2/m) ~ he invention iB not limited, neither to the specific mode of the operations gi~en in the examplel nor ta the compoBition of -khe aluminium. It iB alBO poSBible, without exceeding the scope o.~ the present invention, to use, ~8 an aluminium with precipitatable alloying element~, the alloys Al-~u, Al-Cu-Mg, Al-Zn-~g, Al-Zn-Mg-Cu and Al Mg 5i.

Claims (14)

Claims:

1. A process of manufacturing of wire rods of precip-itation hardenable aluminium, the process comprising a first exclusively thermic step in which a continuous bar of said aluminium is quenched in a continuous process down to a quenching temperature whereby a restored structure is obtained with the alloying elements in supersaturated solution, characterized by a second step, thermo-mechanical and downstream the first one in a same continuous operation, in which said bar is worked at an aging temperature, and by the fact that the so obtained wire rods are subsequently, before any subsequent working, submitted to an aging operation.

2. A process according to claim 1, wherein said aging operation is conducted during a free cooling to the ambient air of said wire rods immediately after said working step at aging temperature.

3. A process according to claim 1, wherein said aging operation is conducted during a slowed-down cooling of the wire rods, immediately after the working at aging temperature.

4. A process according to claim 1, wherein said aging operation is conducted by keeping the wire rods, by heating, at aging temperature, immediately after the working at aging temperature.

5. A process according to any one of claims 1 to 3, wherein the working at aging temperature is a rolling operation with reduction of the cross-sectional area.

6. A process according to claim 1, wherein the con-tinuous bar used at the start of said first step is a bar which leaves a hot forming instrument.

7. A process according to claim 6, wherein said hot forming comprises a continuous casting operation which delivers an aluminium skein which is directed towards the entry of a rolling mill, and a hot rolling opera-tion by which the cross-sectional area of said skein is reduced for forming said bar.

8. A process according to claim 7, in which the entrance temperature of said skein is a temperature higher than the solution treatment temperature.

9. A process according to any one of claims 1 to 3, wherein the aluminium that is used is an alloy Al-Cu, Al-Cu-Mg, Al-Zn-Mg, Al-Mg-Zn-Cu and Al-Mg-Si.

10. A process according to any one of claims 1 to 3, wherein the said bar is quenched in the first step to an aging temperature.

11. A process according to claim 1, wherein the aluminium comprises 0.3 to 0.9% of magnesium, 0.25 to 0.75% of silicon and 0 to 0.60% of iron, the balance being aluminium and impurities.

12. A process according to claim 11, wherein in said second step, the bar is worked at a temperature ranging from 130°C to 260°C.

13. A process according to claim 12, wherein said bar is worked in a continuous rolling mill, which is left by the wire rods at an exit temperature ranging from 155°C to 185°C, and that the wire rods are coiled up and that the so formed coils are subsequently cooled down in a closed container.

14. A process according to claim 13, wherein the con-tinuous bar used at the start of said first step is a bar which leaves a continuous rolling mill in which the aluminium is worked at a temperature which varies from a temperature exceeding 470°C at the entrance of the rolling mill down to a temperature not lower than 350°C at the exit.