For years now, Alcoa (NYSE:AA) has had to deal with mixed economic conditions in the key industries that it serves, with sluggishness in the overall global economy contributing to poor prospects that have held the aluminum specialist's share price in check. Coming into Wednesday afternoon's second-quarter financial report, Alcoa investors wanted evidence that the company's long-awaited turnaround efforts had finally started to take root and made themselves clear in better results. Yet while some of Alcoa's numbers looked promising, the company didn't deliver the unambiguous earnings surprise that investors had wanted to see. Let's look more closely at the latest results from Alcoa and what to expect next for the aluminum-maker for the rest of 2015 and beyond.

Alcoa tops revenue estimates, but earnings fall short
As we've seen in previous quarters, Alcoa's second-quarter numbers showed modest improvement compared to past figures, but they didn't show the acceleration in growth that the company has strived to achieve. Sales rose 1% to $5.9 billion, defying expectations for a slight contraction in revenue. Yet even though net income climbed slightly, a rise in average share count produced a small drop in GAAP earnings per share. Even after adjusting for special items, a 16% gain in adjusted net income produced only a single penny's growth to $0.19 per share, falling well short of the $0.23 per share that investors following the stock had wanted to see.

Alcoa's major business divisions once more showed disparate performance. Gains in after-tax operating income from the premium Engineered Products and Solutions division amounted to 4%, helping the company reach a record level of profitability for the segment. Global Rolled Products also enjoyed solid performance, with a 9% year-over-year gain in operating income. Productivity gains and the positive impact of completed acquisitions helped boost profits on the value-add side of the business, while huge growth in automotive-related shipments and similar gains in transportation and aerospace more broadly helped boost demand for rolled products. The biggest increases came from the Alumina segment, where operating income jumped more than five-fold to $215 million.

Holding the company back this quarter, though, was the upstream Primary Metals business. Alcoa saw about a 30% drop in operating income from the segment, with weakness in aluminum pricing more than offsetting the lower cost of raw materials and energy necessary to make its products. Realized prices for the segment were down 5% from last year's second quarter, contributing to a big drop in operating margins.

Despite the mixed results, Alcoa CEO Klaus Kleinfeld reminded investors of the long-term perspective. "We continue to transform Alcoa, "Kleinfeld said, "and paired with our innovations, we are cementing Alcoa's position as a premier aerospace and automotive partner."

Waiting for more growth
Alcoa remains optimistic about the long-term prospects of its target-customer industries. For aerospace, the company reduced its growth guidance to a range between 8% and 9%, but Alcoa now expects stronger growth of 8% for 2016 and 13% in 2017. A three-percentage-point boost in North American heavy-duty truck sales to 9% to 11% also bodes well for the aluminum giant, but elsewhere across the globe, prospects for the trucking industry look even weaker than before. In most areas, Alcoa remains confident about its overall future potential.

Segment by segment, Alcoa's broader strategic vision is taking shape. The Firth Rixson acquisition is on track to keep boosting Alcoa's overall performance, while bringing in the TITAL titanium business has also shown early signs of success. Expanding its Iowa plant capacity to produce more sheet metal for automotive customers has paid off, and Alcoa is still working at lowering the cost base for its Alumina and Primary Metals divisions to put the company in a better position to deal with relatively low prices in its end markets.

Alcoa investors didn't seem all that impressed by the news, bidding up shares just half a percent in the first hour of trading following the company's announcement. Given that Alcoa stock gave up 5% during the hectic trading session preceding the release of its quarterly results, investors didn't find the reassurances they wanted in the lightweight-metal manufacturer's numbers. In the long run, Alcoa's efforts appear to be paying off, but until the reality starts showing up in the company's quarterly numbers, it might be hard to convince shareholders that Alcoa's turnaround is for real.

Dan Caplinger has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.