CN101880802B - Al-Mg high magnesium alloys for automobile body sheets and manufacturing method thereof - Google Patents

Abstract

The invention provides Al-Mg high magnesium alloys for automobile body sheets and a manufacturing method thereof, belonging to the technical field of alloy materials. The invention solves the following problem: the existing 5083 series alloys have insufficient strength and poor impact resistance and surface quality when being used for the automobile bodies. The alloys comprise the following components in percentage by weight: 0.01-0.2wt% of Cu, 0.6-0.9wt% of Mn, 4.9-5.6wt% of Mg; 0.05-0.2wt% of Cr, 0.1-1.5wt% of Zn, 0.005-0.01wt% of Be, 0.05-0.2wt% of Ti, 0.05-0.2wt% of Zr, not more than 0.2wt% of Si, not more than 0.3wt% of Fe and the balance Al. The alloys have the advantages of high strength and good plasticity and corrosion resistance.

Description

Al-Mg high magnesium alloys for automobile body sheets and manufacture method thereof

Technical field

The present invention relates to a kind of aluminium alloy and manufacture method thereof, relate in particular to a kind of Al-Mg high magnesium alloys for automobile body sheets and manufacture method thereof, belong to technical field of alloy material.

Background technology

World Auto Industry is faced with three more and more severeer large problems: the energy, environmental protection, safety.Alleviate automotive dead weight with the reduction energy consumption, environmental contamination reduction, the fuel economy of raising automobile, saving limited resources has become the focus that each large automobile factory pays close attention to.Lightweight is an important trend of development of automobile, by substituting traditional ferrous materials with light material, can alleviate the quality of automobile, to reach the purpose of fuel saving.Aluminium alloy has the incomparable premium properties of other materials as the preferred material of automotive light weight technology.

5083 aluminium alloys are high magnesium alloy, and intensity is good in non-heat-treatable alloy, and solidity to corrosion, machinability are good.The anodizing rear surface is attractive in appearance.Electric-arc welding is functional.Main alloy element in 5083 aluminium alloys is magnesium, has good corrosion stability and weldability energy, and medium tenacity.Good corrosion resistance makes 5083 aluminium alloys be widely used in maritime affairs purposes such as boats and ships, and automobile, aircraft weldment, subway light rail, need strict fp pressurized vessel (as liquid tank car, refrigerator car, thermal container), refrigeration plant, TV tower, drilling rigs, facilities for transport and communication, missile parts, plate armour etc.The performance of 5083 aluminium alloys is as follows: tensile strength sigma b (MPa): 〉=270; Offset yield strength σ 0.2 (MPa): 〉=110; Elongation δ 10 (%): 〉=20; Elongation δ 5 (%): 〉=12.

Vehicle body plate belongs to not heat-treatable strengthened alloy with 5083 line aluminium alloys, it is inadequate that its intensity shows slightly, shock resistance is relatively poor, 5083 line aluminium alloys of producing in prior art not only intensity and dent resistance can not satisfy the requirement of car body panel, and a series of new steps or spination deformation bands appear in the common product surface that produces in the deep-draw process, have a strong impact on surface quality, occur ruckbildung after baking vanish, from and make it be unfavorable for aluminium alloy as vehicle body plate.

If take 5083 line aluminium alloys as research object, obtain can be used as the aluminium alloy of vehicle body plate, need to adjust its chemical composition and mass percent thereof.Although the people such as Zhou Qingbo are in the light alloy processing technology, 2007, Vol.35, the impact of chemical components on properties of 5083 aluminium alloy has been described in No10, the role and influence of Mg have specifically been set forth, the role and influence of Mn, the effect of trace element Cr, Ti and on the impact of aluminium alloy capability, impurity F e, the Si impact on aluminium alloy capability, it is higher that but those skilled in the art can't go out intensity according to the content proportioning of the document, shock resistance is better, is not prone to softeningly after baking vanish, can be used as the aluminum alloy chemically composition of vehicle body plate.

Summary of the invention

The objective of the invention is for the existing 5083 existing defectives of line aluminium alloy, provide a kind of take 5083 line aluminium alloys as research object, intensity and tensile property are good, can not occur after baking vanish softening, satisfy plasticity and to Al-Mg high magnesium alloys for automobile body sheets and the manufacture method thereof of shock resistance.

Purpose of the present invention can realize by following technical proposal: a kind of Al-Mg high magnesium alloys for automobile body sheets, and the composition of this aluminium alloy and mass percent thereof are:

Cu：0.01-0.2wt％；Mn：0.6-0.9wt％；Mg?4.9-5.6wt％；

Cr：0.05％-0.2wt％；Zn：0.1-1.5wt％；Be：0.005-0.01wt％；

Ti：0.05-0.2wt％；Zr：0.05-0.2wt％；Si≤0.2wt％；

Fe≤0.3wt%; Surplus is Al.

In prior art, the composition of 5083 aluminium alloys and mass percent thereof are:

Copper Cu :≤0.10wt%; Manganese Mn:0.40～1.0wt%; Magnesium Mg:4.0～4.9wt%; Chromium Cr:0.05～0.25wt%; Zinc Zn :≤0.25wt%; Titanium Ti :≤0.15wt%; Silicon Si :≤0.40wt%; Iron Fe :≤0.40wt%; Aluminium Al: surplus.Although 5083 aluminium alloys have mechanical property and machining property and good corrosion resistance nature preferably, because the scope of 5083 aluminum alloy chemical compositions is larger, when the mass percent value of composition is different, can obtain different material characteristics.

The present invention adds up to take 5083 aluminium alloys as research object the Zr that adds 0.05-0.2wt% on the basis at matrix.In aluminum magnesium alloy, disperse, tiny coherence Second Phase Particles Al have been separated out ₃Zr, its strengthening mechanism is to have produced the strengthening effects such as extremely strong refined crystalline strengthening, substructure reinforcement, dispersion-strengthened and coherence reinforcement in alloy, avoids forming thick second-phase compound, the tissue of refinement material improves the performance of material.

Add certain Zn and Cu in alloy, can be by forming η-MgZn ₂, CuMgAl ₂With Al ₂The disperse of Cu compound distributes and improves alloy strength, can also produce certain ageing strengthening, add the generation that zinc has prevented the stretching slip band preferably in aluminium alloy, be conducive to stamping, after baking vanish, yield strength can not descend, and satisfies preferably the shock proof performance of vehicle body plate.

The present invention is controlled at 4.9-5.6wt% with the mass percent of Mg element, has both guaranteed the intensity of aluminium alloy, has satisfied again its requirement as vehicle body plate plasticity and erosion resistance.The mass percent of Mn element is controlled at 0.6-0.9wt%, not only be conducive to improve the erosion resistance of aluminium alloy, the intensity of aluminium alloy is improved, the mass percent of Cr element is controlled at 0.05%-0.2wt%, the mass percent of Ti element is controlled at 0.05-0.2wt%, can improve the corrosion resistance of Al-Mg high magnesium alloys for automobile body sheets and in castingprocesses hot cracking tendency, simultaneously avoid again reducing the processing characteristics of aluminium alloy.

The present invention has also effectively controlled the content of detrimental impurity Si and Fe, has improved corrosion resistance and the plasticity of aluminium alloy.

In above-mentioned Al-Mg high magnesium alloys for automobile body sheets, the optimizing components mass percent of this aluminium alloy is:

Cu：0.05-0.15wt％；Mn：0.7-0.8wt％；Mg?5.4-5.6wt％；

Cr：0.1％-0.15wt％；Zn：0.8-1.2wt％；Be：0.005wt％；

Ti：0.05-0.1wt％；Zr：0.06-0.1wt％；Si≤0.1wt％；

Fe≤0.15wt%; Surplus is Al.

Another object of the present invention is to provide the manufacture method of above-mentioned Al-Mg high magnesium alloys for automobile body sheets, and the method comprises the following steps:

A, casting: first aluminium ingot is added in crucible electrical resistance furnace, when aluminium ingot fusing and melt temperature are 700-750 ℃, add AlCu50, AlMn10, AlCr4, AlBe3, AlZr4 master alloy and stir; Treat that melt temperature to 710-730 ℃, adds Mg and Zn, slag hitting, refining; Treat that temperature at 710-720 ℃, adds the Al-5Ti-B master alloy, stir and standing 20-50 minute casting in pig mold;

B, homogenizing are processed: the aluminium alloy cast ingot homogenizing of above-mentioned casting is processed hot rolling, process annealing, the cold rolling thin plate that rolls into;

C, annealing: the above-mentioned thin plate that makes is carried out anneal, and the temperature of anneal is 320-420 ℃, and the time of processing is 0.5-2h, makes finished product after anneal.

In the manufacture method of above-mentioned Al-Mg high magnesium alloys for automobile body sheets, as preferably, in steps A in pig mold the temperature of casting be 680-720 ℃.Further preferred, in steps A in pig mold the temperature of casting be 700 ℃.The present invention is take 5083 aluminium alloys as research object, in 5083 aluminium alloys, Mg content is high, the MgO film of bath surface is not fine and close, and (MgO/Mg is 0.78,＜1), oxide film easily breaks or is loose porous shape, gas can enter melt by crack or the hollow joint of oxide film, and air-breathing rate increases in time linearly and increases.Air-breathing rate is also relevant with melt temperature, and melt temperature is higher, and air-breathing property is stronger, and the gas that absorbs in aluminium is mainly hydrogen.Hydrogen is that molten aluminum and water reaction generate, and under certain normal atmosphere, temperature is higher, and the solubleness of hydrogen in aluminium is just larger.When solid-state, hydrogen is dissolved in aluminium hardly.And from solid-state during to liquid state, a sudden change appears in the solubleness of hydrogen in aluminium, this solubleness characteristics jumpy have determined aluminium when solidifying, and hydrogen atom is separated out from metal becomes molecular hydrogen, be present in ingot casting with form loose, pore at last, cause the defectives such as loose, pore, simultaneously, pouring temperature is too high, in 5 line aluminium alloys, the Mg scaling loss is serious, finally affects intensity and the unit elongation of finished product.Pouring temperature is too low, and dystectic second-phase solidifies precipitation, causes ingot casting composition organization department even.During 700 ℃ of castings, air-breathing few, the Mg scaling loss is little, and the master alloy element evenly spreads.

In the manufacture method of above-mentioned Al-Mg high magnesium alloys for automobile body sheets, the temperature that in step B, homogenizing is processed is 450-480 ℃, and the treatment time is 10-24 hour.

The purpose of homogenizing annealing is to do tissue for following process to prepare.It is that dendritic segregation is eliminated, the non-equilibrium phase dissolving precipitates mutually with oversaturated transition element that Main Tissues in homogenizing annealing changes, and the concentration of solute is homogenizing gradually.In the homogenizing annealing process, insoluble superfluous phase also can be assembled, nodularization.During slow cooling, dissolve in the solute of sosoloid under high temperature after homogenizing annealing insulation, will reduce and the rule that reduces by solubility with temperature, the Precipitation more equably in crystal grain inside.Temperature raises diffusion process will be accelerated greatly, for accelerating Homogenization Process, should improve as far as possible the homogenizing annealing temperature.Usually the homogenizing annealing temperature that adopts is 0.9～0.95Tm.Tm represents the actual beginning of ingot casting temperature of fusion, and it is lower than the solidus curve on equilibrium phase diagram.But the 5000 too high Mg scaling loss of line aluminium alloy homogenization temperature oxidations are serious, and coarse-grain causes product intensity inadequate.So the aluminium-magnesium alloy homogenization temperature is generally elected 440-495 ℃ as, when Mg content was higher, temperature was controlled at lower limit.Simultaneously, should guarantee that homogenizing annealing stove fire box temperature is even, preferably deviation is not over ± 10 ℃.Aluminium-magnesium alloy ingot homogenization soaking time general control is at 13-36h, and Mg content is controlled at the upper limit when high, otherwise segregation is difficult to elimination, causes the finished product unit elongation lower.Aluminium alloy Mg content of the present invention is higher, 450-480 ℃, the treatment time be 10-24 hour comparatively reasonable.

In the manufacture method of above-mentioned Al-Mg high magnesium alloys for automobile body sheets, in step B, hot-rolled temperature is 450-480 ℃.The present invention is take 5083 aluminium alloys as research object, and between the thermoplasticity optimal zone of 5083 aluminium alloys, between 440 ℃-480 ℃, excess Temperature can cause the hot-rolled sheet surface oxidation, occurs oxide skin when cold rolling, and Mg content reduces, and intensity and unit elongation reduce; The low temperature rolling meeting causes the hot rolling raw edges serious.So, hot-rolled temperature be controlled at 450-480 ℃ more reasonable.

In the manufacture method of Al-Mg high magnesium alloys for automobile body sheets, as preferably, the cold rolling number of times described in step B is 2-4 time, and the temperature of process annealing is 400-450 ℃, and the time of process annealing is 20min-40min.Further preferred, the cold rolling number of times described in step B is 2 times, and the temperature of process annealing is 420 ℃, and the time of process annealing is 30min.Process annealing is adopted cooling fast, and cooling employing shrend or high wind are cooling fast.Aluminium alloy has higher work hardening, high-magnesium aluminum alloy cold-rolled process intensity obviously raises, form the obvious texture structure of anisotropic, cause when cold rolling raw edges serious, the temperature of process annealing is controlled at 400-450 ℃, after the time of process annealing was 20-40min, texture structure occured to reply softening, strength decreased, can reduce the unnecessary energy consumption of cold-rolled process, rolling pass too much reduces production efficiency, so 2 passages are cold rolling during than heavy reduction, is difficult for producing raw edges after annealing, end properties is good simultaneously, lumber recovery is high, reduces energy consumption, raises the efficiency.

In the manufacture method of Al-Mg high magnesium alloys for automobile body sheets, as preferably, in step C, the temperature of anneal is 350-400 ℃, and the time of processing is 0.5-1h, air cooling after anneal.Further preferred, in step C, the temperature of anneal is 400 ℃, and the time of processing is 0.5h.the present invention is take 5083 aluminium alloys as research object, 5083 abundant recrystallization temperature scopes are 280-400 ℃, Heating temperature is too high, the long meeting of soaking time causes grain growth, cause coarse-grain, be 4.9-5.6% for aluminium alloy Mg content of the present invention, when temperature is higher, soaking time is long, surface oxidation is serious, and crystal grain is grown up rapidly, thereby affect mechanical property and the forming property of finished product, cause Lv Desi slippage and orange peel phenomenon in follow-up car body panel stamping process, so adopt Short-time Annealing at High-temperature technique, annealing temperature is 350-400 ℃, the time of processing is that 0.5-1h is comparatively reasonable.

In sum, the present invention has the following advantages:

Al-Mg high magnesium alloys for automobile body sheets of the present invention is by the control to Mg and Mn element mass percent, can guarantee intensity, the plasticity and corrosion-resistant of aluminium alloy, recrystallization temperature and refinement metallographic structure can be improved by the control to micro-Cr and Ti element mass percent, the reduction of aluminum alloy materials plasticity and erosion resistance can be prevented to the control of impurity F e and Si; Add the strength decreased after a certain amount of Zr, Be can effectively prevent the aluminium alloy baking vanish in alloying constituent, has simultaneously good plasticity, promote that better automobile industry extensively adopts aluminum alloy plate materials to substitute Plate Production body of a motor car stamping parts, satisfy the purpose that realizes energy-saving and emission-reduction, brought very good economic benefit, application prospect is very good.

Embodiment

Below by specific embodiment, technical scheme of the present invention is described in further detail; But the present invention is not limited to these embodiment.

The present invention is take 5083 aluminium alloys as research object, and the composition of material and mass percent thereof are: Cu:0.01-0.2wt%; Mn:0.6-0.9wt%; Mg 4.9-5.6wt%; Cr:0.05%-0.2wt%; Zn:0.1-1.5wt%; Be:0.005-0.01wt%; Ti:0.05-0.2wt%; Zr:0.05-0.2wt%; S i≤0.2wt%; Fe≤0.3wt%; Surplus is Al.

Be preferably: Cu:0.05-0.15wt%; Mn:0.7-0.8wt%; Mg5.4-5.6wt%; Cr:0.1%-0.15wt%; Zn:0.8-1.2wt%; Be:0.005wt%; Ti:0.05-0.1wt%; Zr:0.06-0.1wt%; Si≤0.1wt%; Fe≤0.15wt%; Surplus is Al.

During concrete the manufacturing, alloy raw material adopts electrolysis fine aluminium, 99.99%Mg, 99.99%Zn and AlCu50, AlMn10, AlCr4, AlBe3, AlZr4, Al-5Ti-B master alloy.

Table 1: the mass percent (wt%) of embodiment 1-4 al alloy component

Embodiment 1

Prepare burden according to 1 mass percent of embodiment in table 1, make aluminium ingot, master alloy AlCu50, AlMn10, AlCr4, AlBe3, AlZr4, Al-5Ti-B.

First aluminium ingot is added in crucible electrical resistance furnace, when aluminium ingot fusing and melt temperature are 720 ℃, add AlCu50, AlMn10, AlCr4, AlBe3, AlZr4 master alloy and stir; Treat melt temperature to 710 ℃ to add Mg and Zn, slag hitting, refining; Treating that temperature at 710 ℃, adds the Al-5Ti-B master alloy, stir and standing 50 minutes, is casting in the pig mold of 680 ℃ in temperature;

The aluminium alloy cast ingot homogenizing of above-mentioned casting is processed, and the temperature that homogenizing is processed is 450, and the treatment time is 24 hours, be hot rolling under 450 conditions in temperature, process annealing, the temperature of process annealing is 400 ℃, the time of process annealing is 40min, adopts shrend cooling fast after process annealing.Roll into thin plate cold rolling 2 times;

The above-mentioned thin plate that makes is carried out anneal, and the temperature of anneal is 320 ℃, and the time of processing is 2h, and the air cooling of coming out of the stove after anneal makes the Al-Mg high magnesium alloys for automobile body sheets finished product.

Embodiment 2

Prepare burden according to 2 mass percents of embodiment in table 1, make aluminium ingot, master alloy AlCu50, AlMn10, AlCr4, AlBe3, AlZr4, Al-5Ti-B.

First aluminium ingot is added in crucible electrical resistance furnace, when aluminium ingot fusing and melt temperature are 730 ℃, add AlCu50, AlMn10, AlCr4, AlBe3, AlZr4 master alloy and stir; Treat melt temperature to 720 ℃ to add Mg and Zn, slag hitting, refining; Treating that temperature at 710 ℃, adds the Al-5Ti-B master alloy, stir and standing 40 minutes, is casting in the pig mold of 700 ℃ in temperature;

The aluminium alloy cast ingot homogenizing of above-mentioned casting is processed, the temperature that homogenizing is processed is 460 ℃, treatment time is 20 hours, be hot rolling under 460 ℃ of conditions in temperature, process annealing, the temperature of process annealing is 420 ℃, and the time of process annealing is 30min, adopts high wind cooling fast after process annealing.Roll into thin plate cold rolling 2 times;

The above-mentioned thin plate that makes is carried out anneal, and the temperature of anneal is 350 ℃, and the time of processing is 1h, and the air cooling of coming out of the stove after anneal makes the Al-Mg high magnesium alloys for automobile body sheets finished product.

Embodiment 3

Prepare burden according to 3 mass percents of embodiment in table 1, make aluminium ingot, master alloy AlCu50, AlMn10, AlCr4, AlBe3, AlZr4, Al-5Ti-B.

First aluminium ingot is added in crucible electrical resistance furnace, when aluminium ingot fusing and melt temperature are 740 ℃, add AlCu50, AlMn10, AlCr4, AlBe3, AlZr4 master alloy and stir; Treat melt temperature to 720 ℃ to add Mg and Zn, slag hitting, refining; Treating that temperature at 720 ℃, adds the Al-5Ti-B master alloy, stir and standing 30 minutes, is casting in the pig mold of 700 ℃ in temperature;

The aluminium alloy cast ingot homogenizing of above-mentioned casting is processed, the temperature that homogenizing is processed is 470 ℃, treatment time is 15 hours, be hot rolling under 470 ℃ of conditions in temperature, process annealing, the temperature of process annealing is 400 ℃, and the time of process annealing is 30min, adopts shrend cooling fast after process annealing.Roll into thin plate cold rolling 2 times;

The above-mentioned thin plate that makes is carried out anneal, and the temperature of anneal is 400 ℃, and the time of processing is 0.5h, and the air cooling of coming out of the stove after anneal makes the Al-Mg high magnesium alloys for automobile body sheets finished product.

Embodiment 4

According to the 4 mass percent batchings of embodiment in table 1, make aluminium ingot, master alloy AlCu50, AlMn10, AlCr4, AlBe3, AlZr4, Al-5Ti-B.

First aluminium ingot is added in crucible electrical resistance furnace, when aluminium ingot fusing and melt temperature are 750 ℃, add AlCu50, AlMn10, AlCr4, AlBe3, AlZr4 master alloy and stir; Treat melt temperature to 730 ℃ to add Mg and Zn, slag hitting, refining; Treating that temperature at 720 ℃, adds the Al-5Ti-B master alloy, stir and standing 20 minutes, is casting in the pig mold of 720 ℃ in temperature;

The aluminium alloy cast ingot homogenizing of above-mentioned casting is processed, the temperature that homogenizing is processed is 480 ℃, treatment time is 10 hours, be hot rolling under 480 ℃ of conditions in temperature, process annealing, the temperature of process annealing is 420 ℃, and the time of process annealing is 20min, adopts shrend cooling fast after process annealing.Roll into thin plate cold rolling 2 times;

The above-mentioned thin plate that makes is carried out anneal, and the temperature of anneal is 420 ℃, and the time of processing is 0.5h, and the air cooling of coming out of the stove after anneal makes the Al-Mg high magnesium alloys for automobile body sheets finished product.

Randomly drawing above-described embodiment 1-4 makes the aluminium alloy finished product and at room temperature parks after 3 days and carry out tension test.170 ℃ * 30min of simulation paint baking is to carry out in resistance furnace.

Randomly draw that embodiment 1-4 makes that room temperature after the Aluminium Alloy Plate solid solution that contains a certain amount of Zn and Zr was placed 3 days and baking vanish after performance index compare with performance before and after the Aluminium Alloy Plate baking vanish that does not add mentioned component, see Table in detail 2.

Table 2

By as seen from Table 2, the yield strength before Aluminium Alloy Plate punching press of the present invention is lower, is conducive to stampingly, and after baking vanish, intensity does not reduce, and raises on the contrary, and this aluminium alloy has good shock resistance as vehicle body plate.

Specific embodiment described in the present invention is only to the explanation for example of the present invention's spirit.Those skilled in the art can make various modifications or replenish or adopt similar mode to substitute described specific embodiment, but can't depart from spirit of the present invention or surmount the defined scope of appended claims.

Although the present invention has been made a detailed description and has quoted as proof some specific embodiments, to those skilled in the art, only otherwise it is obvious leaving that the spirit and scope of the present invention can make various changes or revise.

Claims (3)

1. the manufacture method of an Al-Mg high magnesium alloys for automobile body sheets, the composition of described aluminium alloy and mass percent thereof are: Cu:0.05-0.15wt%; Mn:0.7-0.8wt%; Mg:5.4-5.6wt%; Cr:0.1%-0.15wt%; Zn:0.8-1.2wt%; Be:0.005wt%; Ti:0.05-0.1wt%; Zr:0.06-0.1wt%; Si≤0.1wt%; Fe≤0.15wt%; Surplus is Al, and the method comprises the following steps:

A, casting: first aluminium ingot is added in crucible electrical resistance furnace, when aluminium ingot fusing and melt temperature are 700-750 ℃, add AlCu50, AlMn10, AlCr4, AlBe3, AlZr4 master alloy and stir; Treat that melt temperature to 710-730 ℃, adds Mg and Zn, slag hitting, refining; Treat that temperature at 710-720 ℃, adds the Al-5Ti-B master alloy, stir and standing 20-50 minute casting in pig mold;

B, homogenizing are processed: the aluminium alloy cast ingot homogenizing of above-mentioned casting is processed hot rolling, process annealing, the cold rolling thin plate that rolls into; The temperature that described homogenizing is processed is 450-480 ℃, and the treatment time is 10-24 hour; Described hot-rolled temperature is 450-480 ℃; The temperature of described process annealing is 400-450 ℃, and the time of process annealing is 20min-40min; Described cold rolling number of times is 2-4 time;

C, annealing: the above-mentioned thin plate that makes is carried out anneal, and the temperature of anneal is 320-420 ℃, and the time of processing is 0.5-2h, makes finished product after anneal.

2. the manufacture method of Al-Mg high magnesium alloys for automobile body sheets according to claim 1 is characterized in that: in steps A in pig mold the temperature of casting be 680-720 ℃.

3. the manufacture method of Al-Mg high magnesium alloys for automobile body sheets according to claim 2, it is characterized in that: in step C, the temperature of anneal is 350-400 ℃, and the time of processing is 0.5-1h, air cooling after anneal.