Al Si Cu Research Articles

Effect of transition metals on energy absorption during strain-controlled fatigue of an aluminum alloy

Tensile and low cyclic fatigue tests were used to assess the influence of micro-additions of Ti/V/Zr on the performance of Al–7Si–1Cu–0.5Mg (wt.%) alloys in the as-cast and T6 heat-treated conditions and their improvement was compared to the base alloy. The microstructure of the as-cast Al–7Si–1Cu–0.5Mg (wt.%) base and modified alloys consisted of α-Al, eutectic Si, and Cu, the Mg- and Fe-based phases Al2.1Cu, Al8.5Si2.4Cu, Al7.2Si8.3Cu2Mg6.9 and Al14Si7.1FeMg3.3. In addition, the micro-sized Ti/V/Zr-rich phases Al6.8Si1.4Ti, Al21.4Si4.1Ti3.5VZr3.9, Al6.7Si1.2TiZr1.8, Al2.8Si3.8V1.6Zr and Al5.1Si35.4Ti1.6Zr5.7Fe were identified in the modified alloys. It was also noticed that increasing the content of Ti–V–Zr changed the morphology of Ti/V/Zr-rich phase. The tensile test results showed that the T6 heat-treated alloy modified with the addition of a higher content of Ti–V–Zr achieved the highest tensile strength of 343MPa over the base alloy and alloys modified with additions of Ti, Ti–Zr and lower contents of Ti–V–Zr. The plastic strain energy density coefficient of the alloy modified with the addition of a higher content of Ti–V–Zr in the T6 temper condition was higher than the other studied alloys and reached 162MJm−3. The fatigue life of the same alloy was considerably longer than that of the other studied alloys, including the base alloy. The fractography revealed that all the studied alloys showed similar fracture behavior. The tensile cracks propagated through the eutectic Si and primary phases, exhibiting intergranular fracture along with some cleavage-like features of the plate-shaped Zr–Ti–V-rich intermetallics with the presence of fatigue striations on the latter, indicating their ductile nature. It is believed that the morphological changes of intermetallic precipitates containing Zr, Ti and V enhance the fatigue life of the alloy modified with additions of larger amounts of Ti–V–Zr in the T6 condition.

Effect of Mn and heat treatment on improvements in static strength and low-cycle fatigue life of an Al–Si–Cu–Mg alloy

Tensile and low cyclic fatigue properties were used to assess the influence of Mn additions and heat treatment on the performance of the Al–7Si–1Cu–0.5Mg (wt%) alloy. As a reference, the Mn-free base and the currently used automotive alloys A380 and A319 were used. In the as-cast state, the Mn-modified alloy consisted of the α-Al, eutectic Si, and Cu- and Mg-based phases including Al2.8Cu, Al14.9SiCu4.9 and Al13.8Si4.5CuMg4. In addition, the Mn-rich phases of Al59.2Si9.2CuFe3.4Mn6.3, and Al26Si4.1Cu1.1MgFe1.4Mn2.6 were present after casting. During solution treatment, Cu-based phases were completely dissolved, while the eutectic Si and Mg-rich phases experienced partial dissolution. Some of the Mn-rich phases were partially dissolved while the Al59.2Si9.2CuFe3.4Mn6.3 compound transformed to Al15(FeMn)3(Si)2. The Mn-modified alloy after T6 heat treatment achieved an elongation of 13.5% with an ultimate tensile strength of 355MPa, which is ~18MPa higher than the Mn-free base and ~30% higher than the A319 alloy after similar heat treatment. The fatigue life of the Mn-modified alloy was also substantially longer than that of the reference base and the A319 grade. After failure, the Mn-modified alloy exhibited ductile fracture with major cracks propagated through inter-dendritic regions of the primary Al-phase with fragmented intermetallics. It is believed that the Mn-rich dispersoid precipitates, formed as a result of T6 heat treatment, improved performance of the Mn-modified alloy.

Ageing characteristics and high-temperature tensile properties of Al–Si–Cu–Mg alloys with micro-additions of Cr, Ti, V and Zr

Ageing characteristics and high temperature tensile properties of the Al–7Si–1Cu–0.5Mg (wt%) alloy modified with transition metals Cr, Ti, V and Zr, were tested. The modified alloy formed the Cr/Ti/V/Zr-rich dispersoid phases with a variety of morphologies. During isochronal ageing, the alloy reached a peak hardness of 92 HRF after a cycle at 200°C for 1h. The tensile test at room temperature showed that alloying additions increased the yield stress by 30% and ultimate tensile strength by 5%. With increasing the testing temperature from 25°C to 300°C, the yield strength and tensile strength decreased from 300MPa to 184MPa and from 313MPa to 196MPa, respectively. Fractographic analysis after tensile testing revealed that coarse intermetallics influenced the crack propagation. At lower temperature, the cleavage-type brittle fracture was dominant while at higher temperature the fully ductile cracking mode was present. It is believed that the Cr, Zr, Ti and V-containing dispersoid phases improved the alloy strength at the elevated temperature.

Microstructure and mechanical properties of Al–Si cast alloy with additions of Zr–V–Ti

Abstract The microstructure and tensile properties at temperatures up to 300 °C of an experimental Al–7Si–1Cu–0.5Mg (wt.%) cast alloy with additions of Ti, V and Zr were assessed and compared with those of the commercial A380 grade. The microstructure of both alloys consisted of Al dendrites surrounded by Al–Si eutectic containing, within its structure, the ternary Al–Al2Cu–Si phase. Whereas the Al15(FeCrMn)3Si2 phases were present in the A380 alloy, Ti/Zr/V together with Al and Si phases, Al(ZrTiV)Si, were identified in the experimental alloy. As a result of chemistry modification the experimental alloy achieved from 20% to 40% higher strength and from 1.5 to 5 times higher ductility than the A380 reference grade. The role of chemistry in improving the alloy thermal stability is discussed.

Effect of solidification rate and loading mode on deformation behavior of cast Al–Si–Cu–Mg alloy with additions of transition metals

The Al–7Si–1Cu–0.5Mg (wt%) alloy with micro-additions of Ti, V and Zr after varied solidification rates in as-cast and T6 heat treated states was subjected to monotonic tension, compression and cyclic deformation. The solidification rate affected the secondary dendrite arm spacing (SDAS), precipitate size which eventually control the flow stress during compression/tension and cyclic deformation. For the as-cast state, a reduction in the SDAS from 30μm to 18μm caused an increase of the ultimate strength from 354MPa to 367MPa and was accompanied by a slight reduction in the alloy deformability from 42.5% to 41.6%. For the T6 state, the strength increased from 413MPa to 419MPa and deformability reduced from 52.4% to 51.0%. The reduction of SDAS in the above range also caused a substantial increase in fatigue life. According to fractography, the tensile cracks propagated mainly through the eutectic Si and primary phases, exhibiting intergranular fracture along with some cleavage-like features through the plate-shaped Zr–Ti–V–rich intermetallics. The presence of fatigue striations on the plate-shaped intermetallics proved their ductile nature and had a positive effect on fatigue life. The EBSD analysis revealed differences in crystallographic texture and the contribution of dynamic recovery during deformation. The benefits of Zr–V–Ti additions in improving the alloy overall performance in automotive applications are discussed.

Monotonic and cyclic deformation behavior of the Al–Si–Cu–Mg cast alloy with micro-additions of Ti, V and Zr

Monotonic and cyclic tests were used to assess the influence of micro-additions of Ti, V and Zr on the deformation behavior of the Al–7Si–1Cu–0.5Mg (wt.%) alloy in as-cast and T6 heat treated conditions and to compare the results with alloys of similar chemistry described in the literature. The microstructure of the as-cast alloy consisted of α-Al, eutectic Si, and Cu, Mg and Fe based phases Al2.1Cu, Al8.5Si2.4Cu, Al7.2Si8.3Cu2Mg6.9 and Al14Si7.1FeMg3.3. In addition, the micro-size Zr–Ti–V-rich phases Al21.4Si4.1Ti3.5VZr3.9, Al6.7Si1.2TiZr1.8, Al2.8Si3.8V1.6Zr and Al5.1Si35.4Ti1.6Zr5.7Fe were present in the as-cast state. During solution treatment, Cu based phases were completely dissolved, while the eutectic silicon, Fe- and Zr–Ti–V-rich intermetallics experienced only partial dissolution. The monotonic test results showed that the T6 heat treated alloy achieved a tensile strength of 343MPa and a compressive strength of 418MPa. Also, the cyclic yield stress of the studied alloy in the T6 temper condition was higher than the monotonic value and reached 335MPa. The fatigue life of the studied alloy was substantially longer than that of the reference alloy with the same base but lower additions of V, Zr and Ti, reported in the literature. The fractography revealed the tensile crack propagation through the eutectic Si and primary phases, exhibiting intergranular fracture along with some cleavage-like features of the plate-shape Zr–Ti–V-rich intermetallics with a presence of fatigue striations on the latter, indicating their ductile nature. It is believed that the intermetallic precipitates containing Zr, Ti and V improve the fatigue life of the studied alloy in the T6 condition.

Effect of Zr, V and Ti on hot compression behavior of the Al–Si cast alloy for powertrain applications

The uniaxial compression test was used to assess the influence of micro-additions of V and Zr on the hot deformation behavior of the Al–7Si–1Cu–0.5Mg–0.1Ti (wt.%) base cast alloy. The temperature in the range of 200–400°C and, to a lesser extent, strain rate in the range of 10−3–1s−1 affected the flow stress of both alloys with the peak stress of the V and Zr modified alloy being consistently higher. Constitutive equations were employed to evaluate the material constants and to correlate them with the hot deformation behavior. The presence of V and Zr increased the activation energy of the plastic deformation from 282.6kJ/mol to 315.2kJ/mol, supporting improved resistance to hot deformation. As revealed through metallographic examinations, fracturing and re-orientation of the second phase particles occurred during compression. For both alloys, the intermetallic particles experienced substantially more frequent cracking than the eutectic silicon. At the same time, in the modified alloy, both the eutectic silicon and intermetallics experienced less frequent fracturing. The precipitates in the modified alloy were also more resistant to rotation within the alloy matrix as a result of hot deformation. The beneficial role of the transition metals V, Zr and Ti in improving the high temperature performance of cast Al alloys was discussed.

Comparison of the Electromigration Behavior of Al(MgCu) with Al(Cu) and Al(SiCu)

ABSTRACTMg is one of the elements that are regarded as having a beneficial effect on the Al electromigration (EM) lifetime. In this paper, we compare the EM behavior of 0.4 μm wide passivated Al-1%Mg-0.5%Cu, Al-0.5%Cu and Al-l%Si-0.5%Cu lines. Plan-view transmission electron microscopy and focused ion beam imaging reveal that Al(MgCu) film undergoes bimodal grain growth. Auger electron spectroscopy and secondary ion mass spectrometry show a strong surface segregation and a severe bulk depletion of Mg. Additionally the line-width dependence of the rate of the resistivity decay during aging shows also a different behavior for Al(MgCu) compared to Al(Cu) and Al(SiCu). All these findings are consistent with the EM results that Al(MgCu), processed with our experimental conditions, has both the lowest median time to failure and deviation in time to failure. The results are discussed in the light of the effect of Mg addition on the microstructure and of the great surface activity of Mg.