英语翻译THE investigation began in the early 1930s.At that time

英语翻译
THE investigation began in the early 1930s.At that time experimental 'high-strength' aluminium alloys had been developed for aircraft use,but little was known of their corrosion properties after sustained exposure.There were also many new protective coverings for aluminium,such as organic paints and inorganic coatings.The Bureau therefore undertook to investigate the commercial and experimental alloys then available,together with the coatings used for surface protection,by exposing them to various weathering conditions for a period of 20 years.The study thus provides data on the 20-year corrosion resistance of aluminium alloys which in some cases have only recently been converted from experimental to commercial status.
Heat-treated alloys
The alloys studied included thosewhich could be hardened by heat treatment and those not susceptible to heat treatment.Among the latter were aluminium-manganese 3004-H34 and aluminium-magnesium 5254-H34.The alloys amenable to heat treatment included clad and bare aluminiumcopper alloys 2017 and 2024.Other alloys contained nickel,cadmium or copper and cadmium.Aluminiummagnesium-silicon alloys,in which hardening is due to the intermetallic compound,MgSi,were also studied.Specimens 0.75 in.x 9 in.long were exposed in selected locations at Washington,D.C.,Norfolk,Va.,and the Panama Canal zone.The latter constituted the tropical marine atmosphere,whereas Washington and Norfolk were the temperate inland and marine locations.All of the marine specimens were exposed near the shoreline where they were occasionally wetted by spray.Studies were made of the aluminiumcopper alloy 2017 with a number of different finishes.Included were samples of clad and bare 2017—several heat treated by selected methods and some protected with various types of organic or inorganic coatings.
The effects of corrosion on each alloy were evaluated by visual and microscopic examination and by the change in its elongation.The samples were removed at intervals from the racks,beginning three months after the start of the test,and were subjected to tensile tests.The tensile strength and elongation after exposure were compared with values obtained on control specimens.The control values for elongation were obtained by averaging the original values and the values obtained on specimens stored in desiccated containers for comparable periods of time.Statistical analysis showed no significant differences in these values with respect to time of storage,surface treatment or paint coating.The Bureau found that improperly heat-treated aluminium-copper alloys failed by intergranular corrosion and severe exfoliation with no measurable elongation after exposure,while those properly heat treated performed satisfactorily.However,2017,when clad with a thin,low-strength alloy,resisted corrosion very well even if incorrecdy heat treated.

该项研究始于二十世纪三十年代.那时,铝合金的高强度试验用于航空领域.但对于长期暴露条件下,其防腐性能如何却知之甚少.当时为铝材料采取了很多保护性措施,例如有机喷涂和无机镀层.该局于是对能找到的贱合金及其所采用的保护涂层进行研究和试验,使之长时间暴露于各种气象条件下长达二十年之久.这项研究提供了二十年来铝合金防腐方面的数据,有些直到最近才由试验状态转化为商业状态.
热处理合金
这项研究包括那些热处理后易于硬化和不大受影响的合金.硅锰合金3004-H34和5254-H34就属于后者.其他合金包括包括镍、镉或铜镉合金.铝锰硅合金的硬度靠金属间的化合来获得,硅锰金属也在研究之列.0.75英寸乘以9英寸长的试棒被分别露天置放于各个不同选择地点：华盛顿特区、诺福克、佛吉尼亚、以及巴拿马运河流域.巴拿马运河流域属热带海洋气候,而华盛顿和诺福克为内陆温带气候和水上气候.全部水上试棒都置放于岸边附近,偶尔会被水浪打湿.试验包括2017铜铝合金,多种方式表面处理.有电镀和裸露的,有几个用多种有机和无机涂层的保护方式处理过.每种合金的腐蚀效果均由肉眼观察和显微试验以及延伸率来进行评价.实验开始三个月后,每隔一定时间,试棒就被从架子上取走,进行抗拉强度试验.经过腐蚀试验样棒的抗拉强度和延伸率与标准试棒进行比较.标准试棒的标准值是试棒原始值与分别保管于干燥条件一定时间的试棒的平均值.统计数据表明,储存时间的长短以及表面如何进行保护处理,其值都没有显著差异.该局发现,热处理方式不当,暴露后的铜铝合金的确产生粒间腐蚀和测量不到延伸率的情况,而那些热处理得当的试棒有令人满意的性能.不过,2017 仅仅镀了薄薄一层低强度合金,尽管热处理错误,仍然有着非常良好的耐腐蚀性.