Mid Sweden University

Considerable research has been devoted to the development of cathode materials for Al-ion batteries, but challenges remain regarding the behavior of aluminum anodes. Inert oxide (Al2O3) film on Al surfaces presents a barrier to electrochemical activity. The structure of the oxide film needs to be weakened to facilitate ion transfer during electrochemical activity. This study addresses oxide film challenges by studying Al alloy anodes with different iron content. The results reveal that using an anode of 99% Al 1% Fe in a cell increases the cycling lifetime by 48%, compared to a 99.99% Al anode. The improvement observed with the 99% Al 1% Fe anode is attributed to its fractional surface area corrosion being about 12% larger than that of a 99.99% Al anode. This is coupled to precipitation of a higher number of Al3Fe particles, which are evenly scattered in the Al matrix of 99% Al 1% Fe. These Al3Fe particles constitute weak spots in the oxide film for the electrolyte to attack, and access to fresh Al. The addition of iron to an Al anode thus offers a cheap and easy route for targeting the oxide passivating film challenge in Al-ion batteries.

Although ionic liquid electrolytes (ILs) are environmentally unfriendly, they are the most common electrolyte used in aluminum-ion batteries (AIB). Aqueous electrolytes offer a more sustainable alternative, but problem with oxide passivating barrier on Al surface becomes more profound. Recently, a new sub-class of aqueous electrolytes, water-in-salt (WIS) of (AlCl3·6H2O), has been considered, but experimental validation of the behavior of the Al electrode over cycling is required. This work investigates aluminum/graphitic cells using WIS electrolytes with a mass ratio of salt to water of 4, 8, and 12 and finds that they show similar trends in cycling performance. The degradation observed over cycling has been attributed to the formation of a detrimental solid electrolyte interphase (SEI) layer on the Al surface. It was found that WIS 4 increased Al corrosion, resulting in a slightly higher capacity and longer cycling life. Metallurgical observation showed that the Al matrix has a tendency to initiate corrosion around Al3Fe intermetallic phases in both WIS and ILs. This implies that the presence of Al3Fe particles allows the electrolyte to break the oxide barrier and access the bulk Al. These results suggests that metallurgical treatments are important to enhance the electrochemical performance of AIB.

Chemical composition analysis using sampling practices in as-cast aluminum alloys are not accurate enough. Optical emission spectrometry (OES) analyses of samples taken at specified milling depths do not match the desired nominal composition due to segregation phenomenon. Moreover, macrosegregation profiles within samples cast with current molds often exhibit significant variations. Various types of molds have been tested in the past to solve this problem, but none have had a satisfactory outcome. This paper presents research on a novel mold with an insulated periphery designed to yield more accurate sampling tests. The results from samples made with the insulated periphery mold show segregation profiles with good reproducibility. A value close to the nominal composition was observed at 6–7 mm milling depth. The reproducibility of segregation profiles is correlated to one-dimensional solidification, minimizing surface segregation areas, and melt convection.

Severe hot tearing has been observed during DC casting of modified AA3000 alloys with additions of Cu, Ti, and Zr, although these alloys are regarded as rather easy to cast. Extensive studies have been performed on both synthetic and industrial AA2000, AA6000, and AA7000 alloys, but less data are available for AA3000 alloys. This work was thus initiated to investigate the hot tearing susceptibility of AA3000 alloys with varying alloy element content using constrained rod casting molds. The results showed that the Cu and Fe content have a major impact on hot tearing resistance, while the effects of Zr and Ti are minor. Cu in a range from 0.3 to 1.2 wt pct significantly increased the hot tearing tendency. This is due to the existence of high eutectic fractions at low temperatures, as well as porosity formation associated with bad feeding at the end of solidification. A strong cracking tendency was observed below an Fe content 0.2 wt pct owing to decreased precipitation of the Al6(Mn, Fe) phase. It was found that primary Al6(Mn, Fe) phases lead to early bridging between the grains, which reinforces the alloy during the vulnerable temperature range for hot tearing. Zr and Ti additions weakly enhanced or reduced hot tearing severity, respectively.

The dissolution of Mn and Fe in liquid Al presents a challenge due to their high melting points and low diffusivity. A literature review reveals that the existing knowledge of the processes involved in the dissolution of both Fe and Mn in liquid Al is rather ambiguous. Thus, this work aimed to obtain more detailed insights into the dissolution behavior of Mn and Fe in various Al melts. The results of the Mn dissolution tests showed that three intermediate phases were involved in the dissolution process, all of which exhibited a smooth interface between Mn and the liquid. These three phases were identified as the γ2, Al11Mn4, and µ phases which grow slowly, penetrating the Mn particles. The results of the Fe dissolution tests showed that in pure Al, the Al5Fe2 phase dominates the dissolution process and penetrates the Fe particles. The addition of Ti into the molten Al alters the intermetallic compound formation by replacing Al5Fe2 by Al2Fe. The addition of Si significantly inhibited the Fe dissolution kinetics. A theoretical approach based on Ficks’ law was used to explain the experimentally obtained Mn and Fe dissolution rates. It showed that the surface area and shape of the additives significantly affected the dissolution processes.

The β-Al5FeSi intermetallic phase and coarse Mg2Si particles have negative effects on extrudability and workability of 6xxx Al alloys billets. To achieve extruded products with a high surface quality, the as-cast billets are heat-treated before extrusion. During heat treatment, the undesired intermetallic particles, i.e., β-AlFeSi platelets are transformed to rounded α-Al(FeMn)Si intermetallic phases. Although the heat treatment of the bulk areas of the 6xxx Al alloys has been the focus of many previous studies, the process of phase transformation at the very surface has not been paid the same attention. In this study, microstructures of a homogenized billet of a 6082 alloy at the area very close to the surface were investigated. By comparing the X-ray diffraction patterns (XRD) of heat-treated samples as a function of different holding times, the gradual phase transformations could be followed, and using GDOES and map analysis by EDX, the alloying elemental redistribution was analyzed. Partial remelting and porosity growth was detected, and transformation rates were faster than in bulk material and from what is known from industrial processes.

Intermetallic β-Al5FeSi phase and coarse Mg2Si particles have negative effects on extrudability and workability of 6xxx Al alloy billets. To achieve extruded products with a high surface quality as-cast billets are therefore heat-treated before extrusion. During heat treatment the undesired intermetallic particles, i.e., β-AlFeSi platelets, are transformed to a rounded α-Al(FeMn)Si intermetallic phase. This transformation was studied in-situ by TEM for 6005 and 6082 Al alloys. It was observed that the Mg2Si particles precipitate in the Al matrix at about 250 °C; this precipitation also occurred at the edge and faces of beta intermetallic particles, and the Mg2Si particles were the preferred sites for α-Al(FeMn)Si particle nucleation. The transformation proceeded faster and at lower temperatures, 350–450 °C, than what has been reported earlier for homogenization studies of bulk samples and industrial billets. This could be associated with the thin characteristic of used samples in TEM giving contribution from fast surface diffusion, but it was also concluded that the phase boundary layer diffusion was important for the understanding of how the transformations proceed.

Aluminum alloys of AA3003 are widely used in heat exchangers. This type of alloy mainly contains manganese as alloying element, but in recent developments there have been additions of both titanium and copper. The limits of Mn solubility in aluminum are influenced by these additions, which can cause the formation of large particles of an unwanted AlMnTi phase.

This project was initiated to investigate the effects of Mn contents in combination with Ti additions on the solidification and precipitation behavior using both Bridgman directional solidification and DTA equipment. The results show that coarse AlMnTi particles start forming when Mn contents are over 1.5 wt% in alloys with 0.14 wt% Ti and that the amount significantly increases with increasing Mn content from this level. Large particles were also found for Mn contents slightly below 1.4 wt%. If the Ti additions were on the level of 0.25 wt%. The DTA experiments show that AlMnTi phases grow in a limited temperature interval, and can reach a size of 150 microns. Such large sized particles are detrimental for the material in the ensuing rolling operation and must be avoided, and it is, therefore, important to accurately control the combinations of Mn and Ti contents.

Steel has been the material of choice for automobile manufacturers. In the recent years material such as aluminium and its alloys are taking over the market because of their light weight. The use of aluminium, in automobile manufacturing can result in overall fuel efficiency. Spot welding aluminium alloys require higher electric power and less welding time as compared to steel. Welding guns that can produce an electric current which is approximately 2 to 3 times higher, as compared to steel are required for spot welding aluminium. An efficient method of spot welding Aluminium alloys with the preheating process has been proposed in this paper. Preheating Aluminium sheet before spot welding reduces the thermal and electrical resistance which brings down the electric current requirement to spot weld Aluminium structures. Both spot welding and induction preheating process have been modelled in this paper. The test results of the preheating process have also been verified with practical heating trials. The preheating is performed on-the-fly in advance to spot welding process. The results show that spot welding Al 6082 after preheating up to 200 degrees C, the output current requirements to make the spot weld are reduced by 22%..