The major awkwardness when joining AA2014 lies in the presence of creation of oxide films and brittle intermetallic in the bond region. However, diffusion bonding can be used to join these alloys without much difficulty. This paper reveals the characterization of diffusion connection of aluminum alloy AA 2014 with and without applying copper powder. Joining was achieved in vacuum up to (1 × 10 -5 mbar) by means of vacuum system. Aluminum alloy AA2014 samples w ere done as cylinder form and interlayer thickness was equal 100 μm, under joining conditions of (325 °C - 475 °C ) and 4 MPa and period of (1 hour). The ultimate strength was found equal to 188.36 MPa. Bonding joint w as examined using light microscope, (SEM) with (EDS) for determining microstructure and depth of diffusion and microhardness was also used at connection zone. XRD outcomes display that the main intermetallic compound phase formula was Al 2 C. The maximum depth of diffusion obtained was 19.1 μm.
In numerous engineering scopes, Al and its alloys are widely employed as suitable materials for constructions wanted to be lightened. AA2014 alloy is vital for army vehicle and aerospace requests [
In this investigation, the base metals used was AA2014. Pure copper powder with particle size of 14 - 25 µm was utilized as interlayer. The chemical composition and physical properties of base metals and interlayer are tabulated in
The aluminum alloy AA2014 was received as rods with 15 mm diameter. Then,
Alloy | Si | Fe | Cu | Mn | Mg | Cr | Zn | Ti | Pb | In | Al |
---|---|---|---|---|---|---|---|---|---|---|---|
2014 | 0.81 | 0.7 | 4.4 | 0.8 | 0.5 | 0.1 | 0.25 | 0.15 | - | - | Bal. |
Cupowder | - | - | 99.80 | - | - | - | - | - | 0.125 | 0.075 | - |
Alloy | Purity % | Liner Thermal expansion (μm/˚C) | Density g/cm3 |
---|---|---|---|
AA2014 | 23 | 2.8 | |
Cu powder | 99.8 | 17 | 8.96 |
cut into 35 mm length of cylinder portions via wire cutting device. The surface of samples has been produced by polishing and grinding processes to get appropriate flat surface for joining. The joining surface of the AA2014 samples has been grinded by employing diverse sets of (SiC) paper thereafter polished by means of diamond paste 0.3 µm grain size. Surface roughness portable device has been used to measure the roughness of surface after grinding and polishing. The amount of the surface roughness of the wholly samples is (0.5 μm). Cleaning the specimens with acetone was done by using ultrasonic bath device for 15 min to remove any contaminations adhering on it. The copper powders interlayer with 0.158 g weights, according to the mass equation of 100 µm thicknesses and density of powder, was place on surface of sample and sprinkled by alcohol to hold the powder.
The polished and chemically prepared specimens of a similar AA2014 aluminum alloys were stacked in a holder and fixture shown in
of diffusion vacuum pump, vacuum tube furnace, rotary vacuum pump, cooling and heating system, control and loading unit. The practical load used for joining the samples by means of hydraulic kind (mega-Spanish) of size 50 ton that has servo motor, it should be noted that (each 1 ton is equivalent to 56 MPa according to cross section area of 176.6 mm2 of sample in this work).
The bonding process was conducted at 325,375,425,475˚C under a vacuum of 1 × 105 m bar and holding pressure of 4 MPa for constant period (one hour). Tensile strength test has been carried out for the bonded specimens.
Diffusion bonding samples have been prepared thru wire cut apparatus into flat tensile test samples as stated by (ASTM E8-8) [
To examine the mechanical properties of the bonded specimens, uniaxial tension checks were achieved.
From
The influence of temperature on joining strength with and without using interlayer is clarified in
Microhardness examination has been achieved for the testing sample diffusion bonding joint. The microhardness was computed at base metal and bonding area. The examination starts from the left side to the right side of the base metal passing through the interlayer with 0.2 mm spaced points.
Experimental No. | Interlayer | Bonding T (˚C) | Bonding P (MPa) | Fracture location | Ultimate strength (MPa) |
---|---|---|---|---|---|
1 | None | 325 | 4 | At interface | 118.55 |
2 | None | 375 | 4 | At base metal | 129.17 |
3 | None | 425 | 4 | At interface | 139.74 |
4 | None | 475 | 4 | At interface | 150.40 |
5 | Copper powder | 325 | 4 | At base metal | 187.05 |
6 | Copper powder | 375 | 4 | At base metal | 187.49 |
7 | Copper powder | 425 | 4 | At base metal | 187.93 |
8 | Copper powder | 475 | 4 | At base metal | 188.36 |
the microhardness at the best conditions; the microhardness measured recorded (89 Hv) at base metal and enlarged progressively up to (109 Hv) nearby the interlayer. The microhardness measurement is (127 Hv) at interlayer which is superior than of base metal inasmuch as the interlayer is pure powder of copper and has higher hardness than the base metal. Thereafter, the microhardness thru the interlayer in the direction of the base metal on the right of bonding region commenced to reduce. The measurements were (97 Hv) and reduce to (85 Hv) at base metal. The cause for this difference was owing to the high hardness of the Cu powder that was greater than other areas.
OM and SEM are utilized for the valuation of the microstructure of diffusion bonding joint achieved at 425˚C, and 4 MPa thrua period of one hour using Cu powder interlayer.
The significant factors for diffusion atoms in the diffusion bonding procedures were diffusion coefficient, sufficient time, pressure and temperature applied. The diffusion process needs appropriate time to happen and when the atoms are large further time is required to get a homogenous structure [
The diffusion coefficient for copper is equal to 6.54 m2s−1 × 10−4. The Cu interlayer exposed the supreme tensile strength inasmuch as the upsurge in the
creating of Al2Cu phase which grants the improvement of mechanical properties [
The bonded joint was tested using EDS at diverse points is exposed in
The EDS line for best conditions joint regions has been inspected as shown in
Points | Al | Cu | Mg |
---|---|---|---|
1 | 0 | 100 | 0 |
2 | 19.1 | 80.9 | 0 |
3 | 49.1 | 50.9 | 0 |
4 | 86.7 | 12.3 | 1 |
5 | 94.3 | 4.6 | 1.1 |
to in perfect bonding. The extreme deepness of diffusion of Cu atoms in the direction of base metal on both sides of diffusion region is nearly 19.1 µm. The diffusion deepness is elevated because the high free energy of the powder body, unstable and accompanying with existence of actual large internal interface [
In
particles of copper diffused into Al alloy caused an upsurge in mechanical properties and intimate contact among the same alloy this was as a consequence of the increased creation of phases percentage of Al2Cu [
1) Bonding joint of aluminum alloy AA2014 with powder interlayer of Cu powder is better than without ones.
2) The best bonding conditions of diffusion bonding process are as pressure of 4 MPa, temperature of 475˚C and bonding duration one hour. This condition resulted in tensile strength of 188.36 MPa.
3) The microhardness of the diffusion zone is more than of base metal since the hardness of copper is higher than of aluminum alloy AA2014.
4) Maximum deepness of diffusion of copper powder into aluminum alloy AA2014 was about 19.1 µm.
The authors express their gratitude to Mustansiriyah University, College of Engineering, Department of Materials Engineering (Mustansiriyah.edu.iq) Iraq, Baghdad for its support in the preparation this paper.
The author declares no conflicts of interest regarding the publication of this paper.
Saleh, A.A. (2019) Microstructure and Strength of Diffusion Bonded 2014 AA Alloys Using Copper Interlayer. Open Journal of Applied Sciences, 9, 342-353. https://doi.org/10.4236/ojapps.2019.95028