Mao Treatment of Aluminum Alloys

MAO Treatment of Aluminum Alloys
for Personal Armor

А. Dementiev1, B. Shor1, V. Berezyuk2, A. Sinichkin2

1 Company " VEDA STA", Krasnoyarsk, Russia

2 Federal University of Siberia, Krasnoyarsk, Russia

The article examines certain aspects of MAO application for Personal Armor using aluminum alloys. Coating was performed with an experimental installation.

Despite wide useof MAO indifferentindustrial sectors, theoreticunderstanding of natural phenomena underlying it is far from being perfect. Various coatingsare usednowadays.As a rule, they were developed empirically and are quite effective. However, in our view the, industrial application of the technology, particularly on extensive surfaces, is hampered by its power intensity and a number of other process limitations.

Themost well-testedMAOapplicationsusethe currentdensityof 20A/dm2at 380V. Theyrequire 3.5 to 4 hours to fabricate a coat of 0.2 to 0.3 mm thick. However, theprocessconsumes so much power that oftentimes expensive titanium becomes more cost-effective and a better choice for quality fabrications.

Theprocesscanbeconsiderablyimprovedbyoptimizing its operability through combinedinnovationsinpulse- generatingcircuits, electrodes, coolingsystem etc. Theresulting MAOinstallationmaintainedunsophisticatedandreliabledesign,lower powerintensity (decreased from 20A/dm2 to 5 A/dm2), equal distribution of amperage among three phases (with possible migration to the phase –zero plan), lower cost of electrolyte cooling etc.

Withoutgoingintodetailsoftheproprietarytechnology, characteristics of the MAO treatment were considerably improved, in particular the top coat hardness of at least 65 HRC, the coat thickness of around 5 to 300 μm, and the growth time of 0.1 to 1.5 μm per minute.

The following analysis led us to consider personal armor to be oneofthemostpromisingareasforthetestedMAOinstallationandtechnology.

Improvedperformanceofsmallarmsandammunition made ballisticvestslessadequatefor protection if light weight, good ergonomics and affordability are to be maintained. However, recenteventsdemonstratedan acutedemand (both technical and social) in improved and affordable personal armor of type II and III.

Thedominanceofcertaintypesoffirearmsin a particular region underlies the protectionrequirements.For Russia, CIS and former socialist countries the focus is on new ballistic protection against TT guns (protection type II) and AKM automatic machine-guns (protection type III). The preliminary analysis of personal armor is based on armoring materials of Russian manufacture. Asarule, this is heavy steel or very expensive titanium and ceramic plates.

Ourcalculationsprovedpowder, grain, andcastaluminumalloystobemoreefficiently usedwhenshearstrainiscreatedonawiderangeandathighhydrostaticpressure (combinationofpressureandtorsionin the deformation zone) followed by the MAO treatment of members. This determined our subsequent research.

When comparing personal armor materials, the main criterion is an areal density. Inothertermsthisamass (weight) of a unit of area that provides a given level of protection (for instance the mass of 1 dm2ofarmor). The less this value is, the lighter, and therefore, the better the armor becomes. Consideringthatballisticvestscanvaryintheir designfrom 15 to 57 dm2 of armor area, the areal density also determines their comparative cost efficiency.

Anextensiveresearchhasbeenconductedinthe MAOtreatment of different aluminum alloys for their subsequent use in protective armor. Positiveresultsweredemonstratedforaluminumalloyswithhighsiliciumcontent. They allowed lowering the areal density for aluminum alloys to the level of steel (165 g/dm2). Subsequenttestsdecreasedthis value furtherto the level of titanium (approximately 145 g/dm2) while maintaining lower costs. TheFigs. 1–3show the ceramic layer microstructure in one of the test samples. Itistakenwith scanning electron microscope JEOLGSM-7001-F.

Thedetailedcostanalysisof member fabrication revealed that up to 70 % of its cost is comprised by electric power. Therefore,highercostefficiencywaspursued not onlythrough theuseofcheapersubstratematerials (possibly industry-standard aluminum grades), study of the coating structure, its phase composition, porosity etc., but also the correlation between coat characteristics and the oxidation process with a view to further decreasing the power intensity of member treatment.

Itispredictedthattheweightofasinglemember (memberpackage) will fall within 130 g/dm2range (which is at least 5% lighter that titanium). Therefore, providedthatpowerintensityisreduced, forinstance, tohalfitsvalue,thetotalcost of a member (member package) will be within 60 % of a comparable titanium package. Itismorethanasatisfactoryresult.

SincethetypeIIprotectionarmorusedduring the testshaspracticallynoneofthesecondaryimpactfactors, it is undoubtedly preferred over existing ones. Withmoderationfullanalogycanalsobepredictedfor personalarmorofhigherprotection level.

Fig. 1. Ceramic layer microstructure in one of the test samples takenwith scanning electron microscope JEOLGSM-7001-F.

Fig. 2. Ceramic layer microstructure in one of the test samples takenwith scanning electron microscope JEOLGSM-7001-F.

Fig. 3. Ceramic layer microstructure in one of the test samples takenwith scanning electron microscope JEOLGSM-7001-F.