STUDY OF THE EFFECT OF AGING CONDITIONS ON STRENGTH AND HARDNESS OF 6063-T5 ALLOY

STUDY OF THE EFFECT OF AGING CONDITION ON STRENGTH AND HARDNESS OF 6063-T5 ALLOYSupervised by : Dr. G.I.P. De Silva

Presented by :E.M.A.N. Ekanayaka S.A.D.T. Dharmarathna

INTRODUCTIONAluminium - The most abundant metal in the earth crust 8% by weight of the earths solid surface

Properties - Durability, light weight, good extrudability and surface finish

Pure metal and the alloy used as alternatives for other metals (ferrous and non-ferrous), ceramics and wood

Sri Lankan demand Structural applications: Window and Door Frames, Partitioning, L bars, U bars22ALUMEX (PVT) LTD.

Project was industrially focused on Alumex

Product: Extruded Aluminium articles Raw material: 6063-T5 Aluminium alloy

3ISSUESProduction cannot meet the present increased demand

Relatively high cost of products

4PRODUCTION PROCESS5REMEDYReduction of time in the Age Hardening process6OBJECTIVESTo reduce the Age Hardening TimeTo reduce the Energy ConsumptionTo upgrade the Mechanical Properties

7LITERATURE REVIEW 86063-T5 Aluminium alloy6063 Age Hardenable Aluminium alloy Main alloying elements: Mg (0.2 ~ 0.6 wt%) Si (0.45 ~ 0.9 wt%)

T5 - Cooled from an elevated temperature and artificially aged

96063-T5 Aluminium alloySecond Phase: Mg2Si

Solid solubility of Mg2Si decreases from 1.85 wt. % at the eutectic temperature of 595 C

Al-Mg2Si quasi binary system forms

10Age hardeningMaximum hardness is achieved if the precipitates can resist cutting by dislocations, and are too close to permit by-passing of dislocations.Strengthening a metal by introducing small particles of another phase which barriers dislocations motion

Cutting through:When the precipitates are too smallBowing and By pass:When precipitates are too strong to be cut and inter-particle space become large

11The Age Hardening Process12

SSSS

Solution treatment Age hardening treatment Al-Mg2Si quasi binary systemGP zones First form of precipitates (unstable) Needle Shaped with the long axis along [100] of the matrix

Sequence of precipitates in Al-Mg2Si

13

Al-Mg2Si quasi binary systemSequence of precipitates in Al-Mg2Si

phase Developed rod shape with Hexagonal crystal structureMaximum hardness

14Al-Mg2Si quasi binary systemSequence of precipitates in Al-Mg2Si

phase - Equilibrium phase with FCC crystal structureAlloy is over aged Hardness decreases

15Al-Mg2Si quasi binary system16

Closely spaced fine precipitates Resist dislocation Bowing and By pass

Strong large precipitatesResist cutting by dislocations

This is called a Bimodal Precipitate Structure17Closely Spaced Fine PrecipitatesStrong Large PrecipitatesIncreased Hardness+=CONCEPTTwo Step Aging Process18

19Homogeneous Nucleation of a Solute Cluster

r = radius of solute clusterG = free energy needed to form a spherical cluster of radius rGV = change infree energyper unit volume = surface free energy per unit area rc = critical radius of the cluster

Gibbs-Thompson equationr c x lnS = KS = Amount of super saturation at a particular temperatureK = Temperature dependent constant ( K a 1/ T )rc= Critical radius of a cluster at the relevant temperature

When T increases, rc increases

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At temp. T1 clusters nucleate and grow - Size distribution: rmin rmaxWhen temp. is raised from T1 to T2, critical radius is raised from rc1 to rc2 If cluster radius r > rc2, the cluster will survive and continue to grow If cluster radius r < rc2, the cluster will be unstable and will dissolve. But re-nucleation may occur.This results a Bimodal Precipitate Structure with both closely spaced fine precipitates + strong large precipitates, which results better Mechanical Properties.21

Industrially Practiced Age Hardening Process22

Solution treatment Age hardening treatment Process was re-performed within the laboratoryResults were used as reference valuesMeasured Hardness(HV) 47.05Total Time (Age Hardening) 270 minParameters Varied During the Process1st step temperature - T1Time to reach the 1st step temperature - t1Soaking time in the 1st temperature - t22nd step temperature - T2Time to reach the 2nd step temperature - t3Soaking time in the 2nd temperature t4

23T2T1t5t4t3t2t1Temperature (oC)Time (min)LIMITATIONSFurnace LimitationThe industrially acceptable range: 150oC to 250oC

Energy Consumption

Total Time ConsumptionBelow 270 min

24CONSTANTSTime to reach the 1st step temperature: t160 minutes

2nd step temperature: T2225oC

Time to reach the 2nd step temperature: t330 minutes

25T2T1t5t4t3t2t1Temperature (oC)Time (min)STAGE 1 - VARIABLES1st step temperature: T1Altered within150oC-200oC

Soaking time in the 1st temperature: t2Varied from 45 min- 90 min for each set of temperatures

Soaking time in the 2nd temperature: t4Varied Combinations-15 min and 30 min

26T2T1t5t4t3t2t1Temperature (oC)Time (min)All Specimens were Solution Treated

At 540oC for 3 hours

To remove age hardening imposed Dissolve all precipitates

27

Muffle FurnaceA set of combinations among the above variables were developed

Heat treatments were performed using the Super C furnace for 2 samples per combination.28Super C Furnace

Hardness was tested using Vickers Hardness tester 3 per sample 6 per combination Average was recorded

Optimum suitable parameters determined using hardness obtained

29Vickers Hardness Tester

Aging Time and Temperature Combinations 301st step2nd stepHardness(HV)TemperatureTimeTemperatureTime150oC60 min225oC15 min37.85150oC90 min225oC15 min38.25175oC45 min225oC15 min39.10175oC60 min225oC15 min41.68175oC75 min225oC15 min47.58175oC90 min225oC15 min45.93200oC60 min225oC15 min35.05200oC90 min225oC15 min37.87t4 maintained as 15 minT1 varied from 150oC to 200oC T2T1t5t4t3t2t1Temperature (oC)Time (min)Hardness Not Satisfactory31

32t4 maintained as 30 minT1 varied from 150oC to 200oC T2T1t5t4t3t2t1Temperature (oC)Time (min)1st step2nd stepHardness(HV)TemperatureTimeTemperatureTime150oC60 min225oC30 min41.47150oC90 min225oC30 min41.25175oC45 min225oC30 min40.92175oC60 min225oC30 min51.68175oC75 min225oC30 min52.05175oC90 min225oC30 min43.78200oC60 min225oC30 min36.42200oC90 min225oC30 min40.62Reference Hardness (HV) 47.05

DERIVATION1st Step Temperature (T1) : 175oC1st Step Soaking Time (t2) : 60 min

33Rejections 150oC Low hardness in acceptable time duration 200oC Higher energy consumption Current Status1st step temperature : 175oCTime to reach the 1st step temperature : 60 minSoaking time in the 1st temperature : 60 min2nd step temperature : 225oCTime to reach the 2nd step temperature : 30 min

3422517530t4306060Temperature (oC)Time (min)352nd step soaking time t4 was altered 0 ~ 60 min 10 min intervalsDifferent sets of combinations were developedSamples prepared as standard tensile test specimensTensile Test Sample1.72mm(Gauge Length)150 mm14mm66 mmSTAGE 2Heat Treatment - Super C2 specimens per combination

Hardness - Vickers Hardness Tester3 per sample 6 per combination Average was recorded

Tensile Strength Tensile Testing Machine

36Tensometer

Combinations and Results for varied t437Sample noHeat Treatmentt4 (min)Hardness (HV)Tensile Strength (N/mm2)1st Step2nd Step1Reference_47.05228.412175oC - 60 min225 oC - 0 min045.08170.273175oC - 60 min225 oC - 10 min1045.38182.724175oC - 60 min225 oC - 20 min2046.83199.345175oC - 60 min225 oC - 30 min3049.13228.416175oC - 60 min225 oC - 40 min4051.10240.867175oC - 60 min225 oC - 50 min5047.88240.868175oC - 60 min225 oC - 60 min6045.33232.56Graph of Hardness Vs t4 value 38

Graph of Strength Vs t4 value

39TheoreticallyAbsorbed heat energy (E) = mcE= Heat energym = Mass of samplesc = Specific Heat Capacity = Temperature Difference

Since m and c are constant Energy Ratios = Ratio of areas under the graphs

40Temperature (oC)Time (min)Energy ComparisonEFFECTIVENESS Varied t4 41Sample noHeat Treatmentt4 (min)Total Time (min)% Time Saving% Energy Saving1st Step2nd Step1Reference_270002175oC - 60 min225oC- 0 min018033.3345.593175oC - 60 min225oC- 10 min1019029.6339.964175oC - 60 min225oC- 20 min2020025.9334.335175oC - 60 min225oC- 30 min3021022.2228.716175oC - 60 min225oC- 40 min4022018.5223.087175oC - 60 min225oC- 50 min5023014.8117.458175oC - 60 min225oC- 60 min6024011.1111.82Optimum was selected considering above results

422251753040306060Temperature (oC)Time (min)20590Temperature (oC)Time (min)30150Developed Process Process at AlumexHardness (HV) = 51.10Tensile Strength (N/mm2) = 240.86Total Time (min) = 220Hardness (HV) = 47.05Tensile Strength (N/mm2) = 228.41Total Time (min) = 270Microstructure ObservationsMicrostructure Selected sample and referenceViewed using Metallurgical microscope (X200)Idea about grain size43

Metallurgical Microscope44

After optimized Two Step Aging Treatment

Polishing Agent: Polycrystalline Diamond Powder Etchant: 5% HNO3 + 2% HF SolutionMicrostructure Observation

After Alumex Practiced Aging Treatment

Polishing Agent: Polycrystalline Diamond Powder

Etchant: 5% HNO3 + 2% HF Solution

452251753040306060Temperature (oC)Time (min)PROGRESSProperty / parameterPracticed ProcessDeveloped ProcessHardness (HV)47.0551.10Tensile Strength (N/mm2)228.41240.86Total Time (min)270220Time Saving (min)_50% Time Saving_18.52% Energy Saving_23.0846CONCLUSIONConsidering Production Rate, Production Cost and Enhanced Mechanical Properties the following Age Hardening Treatment is recommended.

2251753040306060Temperature (oC)Time (min)THANK YOU47