Study of fatigue crack growth of al 6061-T6 welds obtained by gas metal arc welding along longitudinal direction

Figures & data

Figure 1. (a) Single V-groove GMAW welded butt joint (b) Al 6061-T6 welded plate.

Table 1. Chemical composition of ER-5356 and Al6061-T6.

Alloy	Si	Mg	Cu	Mn	Fe	Cr	Zn	Ti	Al
Al 6061 T-6	0.56	0.98	0.310	0.052	0.2890	0.06	0.0240	0.0180	Rem.
ER-5356	0.25	4.50	0.270	0.050	–	–	–	–	Rem.

Table 2. Welding Parameters of GMAW welding for Al 6061-T6 as per WPS.

Joints
Joint Design: Single V Groove Root Spacing: 1mm
Position		Preheat					Gas
										Percentage Composition
Position of Groove	1 G	Preheat temperature			Room temperature		Shielding			Gases	Mixture (%)		Flow rate(Lpm)
Welding progression	Forward: Yes Backword: Yes	Interpass temperature			50°C					Ar(GMAW)	Argon(purity: 99.997%)		10
Electrical characteristics
		Filler Metal
Weld pass	Process	Class	Dia (mm)		Current type and polarity	Amp (A)		Voltage (V)		Travel speed (mm/min)		Wire-speed (mm/min)
Root run	GMAW	ER 5356	1.2		DCEP	200		21		180		304
Rest pass	GMAW	ER 5356	1.2		DCEP	210		21		180		304
Post weld heat treatments
Temperature: 1800 °C Time: 8 hr. Others: Heating rate:800 °C/hr.  Cooling rate: 800 °C/hr.

Figure 2. Microhardness profile of the GMAW welded Al 6061-T6 specimen.

Table 3. X-ray radiography films.

Sl. No	X-ray films
	Longitudinal direction	Remarks
1		NRI Accepted
2		LOP Not Accepted
3		NRI Accepted
4		NRI Accepted
5		LOP Not Accepted

*Note: NRI -No Recordable Indication), LOP -Lack of penetration.

Figure 3. Universal testing machine.

Figure 4. (a) The detailed specification of tensile and bending test specimens and (b) tensile and bending test specimens.

Table 4. The tensile test result of Al 6061-T6 GMAW welded samples.

	Weld zone				Heat affected zone				Base metal
	1	2	3	Average	1	2	3	Average	1	2	3	Average
Load at yield (KN)	18.27	18.228	19.068	18.52	28.338	27.36	24.33	26.68	31.986	31.77	32.16	31.97
Elongation at yield (mm)	5.840	6.840	6.410	6.36	5.990	5.600	6.940	6.18	7.010	6.390	6.040	6.48
Yield stress (N/mm^2)	163.71	162.808	165.349	163.96	252.973	242.553	217.077	237.53	284.168	283.61	283.598	283.79
Load at peak (KN)	29.730	28.014	29.280	29.1	31.824	32.166	29.628	31.21	36.156	35.976	36.054	36.06
Elongation at peak (mm)	15.600	15.720	15.860	15.73	10.34	10.180	10.010	10.18	12.030	11.73.	11.740	11.89
Ultimate tensile stress (N/mm^2)	266.398	250.214	253.902	256.84	284.11	285.160	264.347	277.87	321.215	321.157	317.937	320.10
Load at break (KN)	29.658	27.966	29.172	28.94	28.11	28.632	25.362	27.37	32.232	33.564	33.858	33.22
Breaking stress (N/mm^2)	265.752	249.785	252.965	256.17	250.937	253.829	226.284	243.68	286.353	299.625	298.571	294.85
% Elongation	15.20	15.28	15.20	15.23	16.50	16.44	15.20	16.05	16.20	16.12	16.30	16.21

Figure 5. Fractured surface of tensile test specimens.

Figure 6. Compact tension test specimen for FCG test.

Figure 7. Location of WZ, HAZ and in Al 6061-T6 GMAW welded plate.

Table 5. The parameters used in the FCG test.

Specimens	Base metal			Weld zone			Heat affected zone
Frequency	10 Hz			10 Hz			10 Hz
Stress ratio (R)	0.1	0.3	0.5	0.1	0.3	0.5	0.1	0.3	0.5
Pre crack length (an) mm	13.0	13.0	13.1	13.9	13.0	12.9	12.9	12.9	11.9
Load range for precrack (ΔP) KN	2.6	2.3	2.3	2.71	3.6	2.9	3.2	3.2	3.5

Table 6. FCG Test result of Al 6061 T-6 GMAW welded specimen.

Zone	R	Kth (MPa√m)	Kc (MPa√m)
BM	0.1	6.483	17.769
	0.3	5.328	15.078
	0.5	5.136	13.691
HAZ	0.1	6.551	16.645
	0.3	6.01	14.08
	0.5	5.117	10.802
WZ	0.1	6.356	14.356
	0.3	5.825	11.679
	0.5	5.684	10.167

Figure 8. da/dN v/s ΔK for BM.

Figure 9. Crack length (a) v/s Number of cycles(N) for BM.

Figure 10. da/dN v/s ΔK for HAZ.

Figure 11. a v/s N for HAZ.

Figure 12. da/dN v/s ΔK for WZ.

Figure 13. a v/s N for WZ.

Figure 14. a v/s N of cycles for R = 0.1.

Figure 15. a v/s N for R = 0.3.

Figure 16. a v/s N for R = 0.5.

Figure 17. da/dN v/s ΔK for R = 0.1.

Figure 18. da/dN v/s ΔK for R = 0.3.

Figure 19. da/dN v/s ΔK for R = 0.5.

Table 7. Fitting constant obtained from experimental data.

Zone	BM			HAZ			WZ
R	0.1	0.3	0.5	0.1	0.3	0.5	0.1	0.3	0.5
C	2.x10-7	4.x10-7	6.x10-7	3.x10-7	5.x10-7	7.x10-7	3.x10-7	5.x10-7	9.x10-7
m	3.12	2.81	2.54	3.53	5.30	3.60	2.87	2.68	5.64

Figure 20. Macro graph of fractured surfaces.

Figure 21. Micrograph of BM. (a) R = 0.1 at Kth region, (b) R = 0.1 at Kc region, (c) R = 0.3 at Kth region, (d) R = 0.3 at Kc region, (e) R = 0.5 at Kth region, (f) R = 0.5 at Kc region.

Figure 22. Micrograph of HAZ. (a) R = 0.1 at Kth region, (b) R = 0.1 at Kc region, (c) R = 0.3 at Kth region, (d) R = 0.3 at Kc region, (e) R = 0.5 at Kth region, (f) R = 0.5 at Kc region.

Figure 23. Micrograph of WZ. (a) R = 0.1 at Kth region, (b) R = 0.1 at Kc region, (c) R = 0.3 at Kth region, (d) R = 0.3 at Kc region, (e) R = 0.5 at Kth region, (f) R = 0.5 at Kc region.

Data availability statement

The author confirmed that the data supporting the findings of this study are within the article. Raw data supporting the findings of this study are available from the corresponding author upon reasonable request.